Trailer connections to Chevrolet Uplander

[golan]

Hello ,
I got a new trailer hook installation (including a 12 pins plug connection) on a brand new 2008 Chevrolet Uplander.
the installer claims that all connections are O.k. , but when I connect my old trailer (7 pin connector) with an adepter (7 to 12 adapter) to the 12 pin plug , I get no brake lights and also the left and right turn lights blinks twice as fast comparing to normal (while the trailer is connected).

The trailer is working fine with my old car (that has a 7pin plug).
I have checked all the outputs (with the 7 to 12 adapter) using a DVM , and all signals (left turn, right turn , brake ,reverse, tail lights) all of them supply the correct signal . but when I plug the trailer , the break signal drops to zero, and also the turn lights goes very fast.

b.t.w. the brake light signal is coming directly from the center break light bulb (and not from one of the sides, like you might think while troubleshooting this problem)

I didn't try to connect the car to a trailer using a 12 pins plug.

I assume it is something that is related to grounds , and also that in American cars the break light share the same bulb as the turn light.

The local installer didn’t succeed solving this problem …after 4 hours of working on the car

Any help will be appreciated from this side of the world.

Thanks
Golan.

[rhandwor]

Use yahoo search type champion trailer wiring. They have wiring diagrams and good pictures. The pirates web site has numerous diagrams.
On my 2000 Silverado I ran a ground from the body ground and two hots all the way back. Two blanks were available for the power. All the rest of the wires were close to the trailer hitch. I used a plug for the connection for the brake unit. The place to plug it in was within 18 inches of the brake pedal.
Appx. 25mm per inch.