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.