Glider Trailer Wiring Tips

Glider trailer wiring can drive you crazy! I finally managed to get
things working, and I offer the following tips in the hope that others
might benefit.

First, you must determine for both the car and the trailer exactly what
turn signal and brake light system is being used. Are there separate
turn signals and brake lights, or are the turn signals and brake lights
combined? The answer is easy if the turn signal lights are amber and
the brake lights are red - they're independent. If the turn signal
lights and brake lights are all red, though, you'll need to look
closely to see if separate bulbs or filaments are used (independent) or
whether the same bulb or filament is used (combined).

Next, you must find out if the car uses a computer. The best bet is the
manual, but another indication is if you get a message on the dash when
a bulb is out (temporarily pull a taillight to find out). If a computer
is used, you'll need to use a powered isolator to prevent possible
destruction of the computer. The isolator will only pull 150 milliamps
from the car's circuitry (too low to bother the computer), but it will
provide full battery power to the trailer (up to 10 amps per light
circuit) for maximum bulb brightness.

With the knowledge from these two steps in hand, here are the four
possibilities and their solutions:

1. If your car doesn't have a computer, and you're going to the same
type of system (independent to independent or combined to combined)
then you can simply wire the appropriate wires inside the car through a
suitable jack and then through a suitable plug to the appropriate wires
inside the trailer. I'd suggest fusing each circuit inside the car for
safety.

2. If your car doesn't have a computer, and you're going independent
to combined, then you need to use a Hoppy Model 48845 taillight
converter for the turn signal and brake light circuits. Again, I'd
suggest fusing each circuit inside the car (before the converter).

3. If your car does have a computer, and you're going independent to
combined, then you can use either a Hoppy 46365 (short proof) or a
Hoppy Model 46255 (non-short proof) powered taillight converter for the
taillight, turn signal and brake light circuits. Again, I'd suggest
fusing each circuit inside the car (but after the converter this time).

4. If your car has a computer and you're going independent to
independent, you have a problem! This is the situation I had with my
BMW and my Cobra trailer. Neither Hoppy or Reese offer a powered
trailer isolator for an independent system, but I found a powered
trailer isolator made by Kriss Motorcycle Products (
http://www.kriss.com/traileri.htm ). I wired it using a 6 pin jack for
the car and a 6 pin plug for the trailer (using only 5 wires), with the
supplied fuses installed between the isolator and the 6 pin jack. This
isolates the taillight, turn signal and brake light circuits of the car
from those of the trailer.

The Kriss isolator worked just fine with the independent system on my
Cobra trailer, but it wouldn't work with my club's trailers - because
they had combined turn signals and brake lights. I needed a taillight
converter, and it seemed like the Hoppy Model 48845 should work. When
it didn't, I experimented and found that all that was needed were three
470 ohm 1/2 watt resistors. Wiring these resistors to the 48845's left
turn input to ground, right turn input to ground, and brake light input
to ground got things working properly. Apparently the outputs on the
Kriss isolator module float until they are powered, and the Hoppy unit
expects to see ground potential on its inputs until they receive power.

Hope this saves someone time and trouble!

-John

P.S. - During this project I learned that some cars use what is termed
a "negative input system". These systems work the reverse of what you
might expect! They don't have the bulbs constantly grounded with power
applied only to light them - instead they constantly provide power to
the bulbs and switch the grounds to light them. I have no experience
with such cars, but I do know that the tips listed above won't work
with them! To determine if you have a negative input system use a
voltmeter to determine if power is always applied to the bulbs.

Wow, Seems complicated, but anything much more than
putting batteries into a flashlight (torch, in UK speak?)
strains my brain when it comes to things electrical.

My tow vehicle, a Honda Accord had a trailer hitch
and wiring installed at a local trailer hitch shop.
The car definitely has computers controlling things.
There is some type of electrical adapter/splice connector
in the trunk (boot) and a 'flat four' connector for
the trailer. The connections are for
1. Ground (earth)
2. Parking lights
3. Left Signal
4. Right Signal

When the brake pedal is applied, the electrical adapter
must provide power to the Left and Right Signal simulataneously
to provide a brake light. And yes, when braking and
signalling, you still have a signal. No, I don't know
how it works, but it works.

I recently bought a NEW Swan trailer and it came with
a round seven pin electrical plug. The rear lights
were Hella units, probably exactly as on a Cobra and
Komet. They are three bulb units with a single lens.
The top bulb is behind an amber part of the lens,
the middle behind a red part, and the bottom behind
another red part of the lens.

I think the top amber lens is for signal, the middle
red is for brake, and the lower red is for parking
lights.

But, since I have only a four wire system, something
had to go, so I figured if I could wire the middle
bulb that is behind the red part of the lens to act
as brake and signal, I would be fine. That would leave
the small bulb at the bottom of the Hella fixture behind
a red part of the lens to work as intended: the parking
light.

All I needed to do was pull off the connector to the
top and middle bulbs. Put the wire that ran to the
top bulb to the middle bulb. The wire that ran to
the middle bulb was just pushed out of the way inside
the Hella fixture. That's it for changes to the wiring
at the left and right fixtures.

Up at the front of the trailer, I had a seven pin round
plug to connect to the flat four plug on my car. Square
pin into the round hole...

Swan provided me with a converter pigtail. On one
end, it had a flat four connector and on the other
was the seven pin connector. Sure, I could have wacked
off the seven pin plug and just wired up the flat four,
but I decided to use the converter 'pigtail' instead.
As shipped from Swan, the 'pigtail' wasn't wired exactly
right, but a few minutes with a screwdriver to disassemble
the plug and put the wires into the right holes had
everything working as I wanted.

The really tricky part, though, was figuring out which
wire up at the seven pin plug went to which light at
the rear of the trailer. Trace the colors, you say?
Well, not exactly. Swan has a junction box up front
on the inside of the trailer and they didn't maintain
a consistant color code. That took me a couple of
hours to figure out because I had forgotten competely
about the junction box. Once I remembered that it
was there and saw the mix of colors, it wasn't too
long before I had it figured all out.

Voila, Success! I had actually won out over those
wrascally electrons.

(At least, there hasn't been any smoke yet...)

Ray Lovinggood
Carrboro, North Carolina, USA
Happy Owner of Swan Trailer

At 21:54 20 June 2006, Jcarlyle wrote:
Glider trailer wiring can drive you crazy! I finally
managed to get
things working, and I offer the following tips in the
hope that others
might benefit.

First, you must determine for both the car and the
trailer exactly what
turn signal and brake light system is being used. Are
there separate
turn signals and brake lights, or are the turn signals
and brake lights
combined? The answer is easy if the turn signal lights
are amber and
the brake lights are red - they're independent. If
the turn signal
lights and brake lights are all red, though, you'll
need to look
closely to see if separate bulbs or filaments are used
(independent) or
whether the same bulb or filament is used (combined).

Next, you must find out if the car uses a computer.
The best bet is the
manual, but another indication is if you get a message
on the dash when
a bulb is out (temporarily pull a taillight to find
out). If a computer
is used, you'll need to use a powered isolator to prevent
possible
destruction of the computer. The isolator will only
pull 150 milliamps
from the car's circuitry (too low to bother the computer),
but it will
provide full battery power to the trailer (up to 10
amps per light
circuit) for maximum bulb brightness.

With the knowledge from these two steps in hand, here
are the four
possibilities and their solutions:

1. If your car doesn't have a computer, and you're
going to the same
type of system (independent to independent or combined
to combined)
then you can simply wire the appropriate wires inside
the car through a
suitable jack and then through a suitable plug to the
appropriate wires
inside the trailer. I'd suggest fusing each circuit
inside the car for
safety.

2. If your car doesn't have a computer, and you're
going independent
to combined, then you need to use a Hoppy Model 48845
taillight
converter for the turn signal and brake light circuits.
Again, I'd
suggest fusing each circuit inside the car (before
the converter).

3. If your car does have a computer, and you're going
independent to
combined, then you can use either a Hoppy 46365 (short
proof) or a
Hoppy Model 46255 (non-short proof) powered taillight
converter for the
taillight, turn signal and brake light circuits. Again,
I'd suggest
fusing each circuit inside the car (but after the converter
this time).

4. If your car has a computer and you're going independent
to
independent, you have a problem! This is the situation
I had with my
BMW and my Cobra trailer. Neither Hoppy or Reese offer
a powered
trailer isolator for an independent system, but I found
a powered
trailer isolator made by Kriss Motorcycle Products
(
http://www.kriss.com/traileri.htm ). I wired it using
a 6 pin jack for
the car and a 6 pin plug for the trailer (using only
5 wires), with the
supplied fuses installed between the isolator and the
6 pin jack. This
isolates the taillight, turn signal and brake light
circuits of the car
from those of the trailer.

The Kriss isolator worked just fine with the independent
system on my
Cobra trailer, but it wouldn't work with my club's
trailers - because
they had combined turn signals and brake lights. I
needed a taillight
converter, and it seemed like the Hoppy Model 48845
should work. When
it didn't, I experimented and found that all that was
needed were three
470 ohm 1/2 watt resistors. Wiring these resistors
to the 48845's left
turn input to ground, right turn input to ground, and
brake light input
to ground got things working properly. Apparently the
outputs on the
Kriss isolator module float until they are powered,
and the Hoppy unit
expects to see ground potential on its inputs until
they receive power.

Hope this saves someone time and trouble!

-John

P.S. - During this project I learned that some cars
use what is termed
a 'negative input system'. These systems work the reverse
of what you
might expect! They don't have the bulbs constantly
grounded with power
applied only to light them - instead they constantly
provide power to
the bulbs and switch the grounds to light them. I have
no experience
with such cars, but I do know that the tips listed
above won't work
with them! To determine if you have a negative input
system use a
voltmeter to determine if power is always applied to
the bulbs.

Ah, well, it's not that complicated.

If your vehicle is not equipped with the factory "towing package", buy the
wiring kit at a dealer's parts counter and install it. My Jeep Grand
Cherokee just required temporarilly removing the right rear interior panel
and pluging the wiring kit into the pre-existing sockets in the vehicle's
main wiring harness. This kit provides a 7-pin round connector which then
requires only an adaptor to a "flat four" connector commonly used on glider
trailers. The Jeep's "Vehicle Information Computer" now informs me of
failed bulbs in the trailer.

Using standard connectors means that any other vehicle can tow your trailer
and you can tow other trailers if needed.

Bill Daniels


"Ray Lovinggood" wrote in
message ...
Wow, Seems complicated, but anything much more than
putting batteries into a flashlight (torch, in UK speak?)
strains my brain when it comes to things electrical.

My tow vehicle, a Honda Accord had a trailer hitch
and wiring installed at a local trailer hitch shop.
The car definitely has computers controlling things.
There is some type of electrical adapter/splice connector
in the trunk (boot) and a 'flat four' connector for
the trailer. The connections are for
1. Ground (earth)
2. Parking lights
3. Left Signal
4. Right Signal

When the brake pedal is applied, the electrical adapter
must provide power to the Left and Right Signal simulataneously
to provide a brake light. And yes, when braking and
signalling, you still have a signal. No, I don't know
how it works, but it works.

I recently bought a NEW Swan trailer and it came with
a round seven pin electrical plug. The rear lights
were Hella units, probably exactly as on a Cobra and
Komet. They are three bulb units with a single lens.
The top bulb is behind an amber part of the lens,
the middle behind a red part, and the bottom behind
another red part of the lens.

I think the top amber lens is for signal, the middle
red is for brake, and the lower red is for parking
lights.

But, since I have only a four wire system, something
had to go, so I figured if I could wire the middle
bulb that is behind the red part of the lens to act
as brake and signal, I would be fine. That would leave
the small bulb at the bottom of the Hella fixture behind
a red part of the lens to work as intended: the parking
light.

All I needed to do was pull off the connector to the
top and middle bulbs. Put the wire that ran to the
top bulb to the middle bulb. The wire that ran to
the middle bulb was just pushed out of the way inside
the Hella fixture. That's it for changes to the wiring
at the left and right fixtures.

Up at the front of the trailer, I had a seven pin round
plug to connect to the flat four plug on my car. Square
pin into the round hole...

Swan provided me with a converter pigtail. On one
end, it had a flat four connector and on the other
was the seven pin connector. Sure, I could have wacked
off the seven pin plug and just wired up the flat four,
but I decided to use the converter 'pigtail' instead.
As shipped from Swan, the 'pigtail' wasn't wired exactly
right, but a few minutes with a screwdriver to disassemble
the plug and put the wires into the right holes had
everything working as I wanted.

The really tricky part, though, was figuring out which
wire up at the seven pin plug went to which light at
the rear of the trailer. Trace the colors, you say?
Well, not exactly. Swan has a junction box up front
on the inside of the trailer and they didn't maintain
a consistant color code. That took me a couple of
hours to figure out because I had forgotten competely
about the junction box. Once I remembered that it
was there and saw the mix of colors, it wasn't too
long before I had it figured all out.

Voila, Success! I had actually won out over those
wrascally electrons.

(At least, there hasn't been any smoke yet...)

Ray Lovinggood
Carrboro, North Carolina, USA
Happy Owner of Swan Trailer

At 21:54 20 June 2006, Jcarlyle wrote:
Glider trailer wiring can drive you crazy! I finally
managed to get
things working, and I offer the following tips in the
hope that others
might benefit.

First, you must determine for both the car and the
trailer exactly what
turn signal and brake light system is being used. Are
there separate
turn signals and brake lights, or are the turn signals
and brake lights
combined? The answer is easy if the turn signal lights
are amber and
the brake lights are red - they're independent. If
the turn signal
lights and brake lights are all red, though, you'll
need to look
closely to see if separate bulbs or filaments are used
(independent) or
whether the same bulb or filament is used (combined).

Next, you must find out if the car uses a computer.
The best bet is the
manual, but another indication is if you get a message
on the dash when
a bulb is out (temporarily pull a taillight to find
out). If a computer
is used, you'll need to use a powered isolator to prevent
possible
destruction of the computer. The isolator will only
pull 150 milliamps
from the car's circuitry (too low to bother the computer),
but it will
provide full battery power to the trailer (up to 10
amps per light
circuit) for maximum bulb brightness.

With the knowledge from these two steps in hand, here
are the four
possibilities and their solutions:

1. If your car doesn't have a computer, and you're
going to the same
type of system (independent to independent or combined
to combined)
then you can simply wire the appropriate wires inside
the car through a
suitable jack and then through a suitable plug to the
appropriate wires
inside the trailer. I'd suggest fusing each circuit
inside the car for
safety.

2. If your car doesn't have a computer, and you're
going independent
to combined, then you need to use a Hoppy Model 48845
taillight
converter for the turn signal and brake light circuits.
Again, I'd
suggest fusing each circuit inside the car (before
the converter).

3. If your car does have a computer, and you're going
independent to
combined, then you can use either a Hoppy 46365 (short
proof) or a
Hoppy Model 46255 (non-short proof) powered taillight
converter for the
taillight, turn signal and brake light circuits. Again,
I'd suggest
fusing each circuit inside the car (but after the converter
this time).

4. If your car has a computer and you're going independent
to
independent, you have a problem! This is the situation
I had with my
BMW and my Cobra trailer. Neither Hoppy or Reese offer
a powered
trailer isolator for an independent system, but I found
a powered
trailer isolator made by Kriss Motorcycle Products
(
http://www.kriss.com/traileri.htm ). I wired it using
a 6 pin jack for
the car and a 6 pin plug for the trailer (using only
5 wires), with the
supplied fuses installed between the isolator and the
6 pin jack. This
isolates the taillight, turn signal and brake light
circuits of the car
from those of the trailer.

The Kriss isolator worked just fine with the independent
system on my
Cobra trailer, but it wouldn't work with my club's
trailers - because
they had combined turn signals and brake lights. I
needed a taillight
converter, and it seemed like the Hoppy Model 48845
should work. When
it didn't, I experimented and found that all that was
needed were three
470 ohm 1/2 watt resistors. Wiring these resistors
to the 48845's left
turn input to ground, right turn input to ground, and
brake light input
to ground got things working properly. Apparently the
outputs on the
Kriss isolator module float until they are powered,
and the Hoppy unit
expects to see ground potential on its inputs until
they receive power.

Hope this saves someone time and trouble!

-John

P.S. - During this project I learned that some cars
use what is termed
a 'negative input system'. These systems work the reverse
of what you
might expect! They don't have the bulbs constantly
grounded with power
applied only to light them - instead they constantly
provide power to
the bulbs and switch the grounds to light them. I have
no experience
with such cars, but I do know that the tips listed
above won't work
with them! To determine if you have a negative input
system use a
voltmeter to determine if power is always applied to
the bulbs.

Does sound very complicated and time consuming. What
I did was contact a local (Sheffield, UK) towbar company
who came and fitted one to my BMW at home for about
£250 towbar, electrics and fitting, and it works just
fine on my Cobra.

Dave Salmon


At 21:54 20 June 2006, Jcarlyle wrote:
Glider trailer wiring can drive you crazy! I finally
managed to get
things working, and I offer the following tips in the
hope that others
might benefit.

First, you must determine for both the car and the
trailer exactly what
turn signal and brake light system is being used. Are
there separate
turn signals and brake lights, or are the turn signals
and brake lights
combined? The answer is easy if the turn signal lights
are amber and
the brake lights are red - they're independent. If
the turn signal
lights and brake lights are all red, though, you'll
need to look
closely to see if separate bulbs or filaments are used
(independent) or
whether the same bulb or filament is used (combined).

Next, you must find out if the car uses a computer.
The best bet is the
manual, but another indication is if you get a message
on the dash when
a bulb is out (temporarily pull a taillight to find
out). If a computer
is used, you'll need to use a powered isolator to prevent
possible
destruction of the computer. The isolator will only
pull 150 milliamps
from the car's circuitry (too low to bother the computer),
but it will
provide full battery power to the trailer (up to 10
amps per light
circuit) for maximum bulb brightness.

With the knowledge from these two steps in hand, here
are the four
possibilities and their solutions:

1. If your car doesn't have a computer, and you're
going to the same
type of system (independent to independent or combined
to combined)
then you can simply wire the appropriate wires inside
the car through a
suitable jack and then through a suitable plug to the
appropriate wires
inside the trailer. I'd suggest fusing each circuit
inside the car for
safety.

2. If your car doesn't have a computer, and you're
going independent
to combined, then you need to use a Hoppy Model 48845
taillight
converter for the turn signal and brake light circuits.
Again, I'd
suggest fusing each circuit inside the car (before
the converter).

3. If your car does have a computer, and you're going
independent to
combined, then you can use either a Hoppy 46365 (short
proof) or a
Hoppy Model 46255 (non-short proof) powered taillight
converter for the
taillight, turn signal and brake light circuits. Again,
I'd suggest
fusing each circuit inside the car (but after the converter
this time).

4. If your car has a computer and you're going independent
to
independent, you have a problem! This is the situation
I had with my
BMW and my Cobra trailer. Neither Hoppy or Reese offer
a powered
trailer isolator for an independent system, but I found
a powered
trailer isolator made by Kriss Motorcycle Products
(
http://www.kriss.com/traileri.htm ). I wired it using
a 6 pin jack for
the car and a 6 pin plug for the trailer (using only
5 wires), with the
supplied fuses installed between the isolator and the
6 pin jack. This
isolates the taillight, turn signal and brake light
circuits of the car
from those of the trailer.

The Kriss isolator worked just fine with the independent
system on my
Cobra trailer, but it wouldn't work with my club's
trailers - because
they had combined turn signals and brake lights. I
needed a taillight
converter, and it seemed like the Hoppy Model 48845
should work. When
it didn't, I experimented and found that all that was
needed were three
470 ohm 1/2 watt resistors. Wiring these resistors
to the 48845's left
turn input to ground, right turn input to ground, and
brake light input
to ground got things working properly. Apparently the
outputs on the
Kriss isolator module float until they are powered,
and the Hoppy unit
expects to see ground potential on its inputs until
they receive power.

Hope this saves someone time and trouble!

-John

P.S. - During this project I learned that some cars
use what is termed
a 'negative input system'. These systems work the reverse
of what you
might expect! They don't have the bulbs constantly
grounded with power
applied only to light them - instead they constantly
provide power to
the bulbs and switch the grounds to light them. I have
no experience
with such cars, but I do know that the tips listed
above won't work
with them! To determine if you have a negative input
system use a
voltmeter to determine if power is always applied to
the bulbs.

I'm glad you had the option, Dave. No towing/trailering outfit over
here in the US would touch my BMW, and the dealer flatly stated "you
can't tow trailers with a BMW". So I was on my own - absolutely no
choice!

By the way, equipping the BMW to tow the Cobra was easy. It took 2
hours once I had the Kriss isolator (the only isolator made, AFAIK,
that isolates independent cars and feeds independent trailers). The
real challenge lay in getting the Hoppy 48845 (needed to drive a
combined trailer off of the Kriss) to work properly! Hoppy engineers
said they had never heard of anyone doing it before - and all it needed
were simple 470 ohm 1/4 watt resistors.

-John

David Salmon wrote:
Does sound very complicated and time consuming. What
I did was contact a local (Sheffield, UK) towbar company
who came and fitted one to my BMW at home for about
£250 towbar, electrics and fitting, and it works just
fine on my Cobra.

Dave Salmon

wrote:

Back in the 1960s, a guy named Tom Page published an article in Soaring
mag trying to establish a standard for trailer wiring (for the record,
it was a widely available round, 4-pin connector). Many, but not all,
pilots adopted that standard at the time.

In recent years, the de facto standard in the U.S. has been either the
flat-four connector to which you refer or the standard 7-pin
German-supplied connector (as mentioned, I subscribe to the
7-pin-connector-with-trailer-factory-wiring school). But there's still
no guarantee that any given tow vehicle/trailer combo will match up
without some late-night fiddling.

Chip Bearden
ASW 24 "JB"

That was the 60s.
I agree that the new standard should be similar to supplied on
European trailers. In the last decade or so have preferred the "6-pin
round" type. It has a metal casing.
US car manufacturers like Ford are still in the 60s with lighting,
choosing to eliminate the brake light circuit to save a few dollars.
It'll be hard to get a decent standard until all the US manufacturers
build cars with internationally acceptable lighting.
At least GM Yukons/Tahoes/Suburbans built 2000 or later went from
4-wire to 5. GM wanted to export them and it's necessary to have amber
turn signals in most countries.

Can't believe the arrogance of John's BMW dealer. It's just a bloody
car. The dealer probably wouldn't approve of taking a BMW X-5 off-road
either!

Jim

There's the possibility that US BMWs made in South Carolina are
different to Bavarian ones.

Always read the owners manual before you buy a car. I won't buy one
unless happy with the list of trailer weights under "Towing". "Towing"
in many car manuals just explains how to move the thing when it breaks!
John found the right solution to this problem: DIY.

The Isolator can't be used as an adapter. It must be installed in the
towing vehicle, as it requires a separate +12V supply for the trailer.
It should be able to synthesize a brake light circuit using the central
brake light of newer vehicles that are "4-wire". In this case both red
and amber trailer lights would come on for brakes.

Jim

JS wrote:
wrote:

Can't believe the arrogance of John's BMW dealer. It's just a bloody
car. The dealer probably wouldn't approve of taking a BMW X-5 off-road
either!

That's BMW for you. All Benz (except coupes) have factory-approved
towbars in the option list and are wired for trailers.

Besides, they were better cars. Some of them still are.

GC

Jim

JS wrote:

Can't believe the arrogance of John's BMW dealer. It's just a bloody
car. The dealer probably wouldn't approve of taking a BMW X-5 off-road
either!

You may be too harsh on the dealer. Some cars are simply not rated by
the factory (German, American, whatever) for towing in the USA, and a
dealer that provides a hitch may be causing himself difficulties with
the factory and his insurance.

This example is old but perhaps pertinent: about 20 years ago, friends
of ours ordered a BMW for the USA, but took delivery in Germany. The
factory would not install the hitch they put on the same model sold in
Europe, nor could our friends find a mechanic in Germany that would do
it either! Eventually, a shop in France agreed to do it, but (as I
recall) with reluctance and "cash only", no paper trail.


--
Change "netto" to "net" to email me directly

Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
Operation"

I bought a new (used) Nissan Pathfinder and needed to add a hitch and a
"four flat" connection to be able to tow my glider trailer.

While I am sure that I could have used a generic trailer wiring cable
kit, I opted to pay for a more expensive cable kit specific to my car.
The nice part about this is that all you need to do is unplug the
connectors to the vehicles lights and then insert matching plugs from
the kit inbetween. Couldn't be simpler. The only difficult part is
getting to the connectors. Of course you have to do that in any case.
I bought the kit online from http://www.etrailer.com/wiring.aspx.

- John

Graeme Cant wrote:
JS wrote:
wrote:

Can't believe the arrogance of John's BMW dealer. It's just a bloody
car. The dealer probably wouldn't approve of taking a BMW X-5 off-road
either!

That's BMW for you. All Benz (except coupes) have factory-approved
towbars in the option list and are wired for trailers.

Besides, they were better cars. Some of them still are.

GC

Jim