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