[cwwozniak]

I am trying to help someone at work get their newly installed trailer's lights to work with their 2007 Yukon. The right side brake/turn light does not come on when the brakes are applied or the turn signal is turned on. I found a pin-out chart for the Yukon's hex shaped trailer connector. There is never any voltage on the combined right brake/turn contact when the brakes are applied or the turn signal is turned on.

The trailer's tail lights and left left brake/turn signal light work fine. All of the lights on the vehicle itself work OK. The left and right turn signal fuses in the fuse box check OK.

I did notice that the right light feed wire in trailer's wire harness looks like it was pinched at one time and has burn marks. Is it possible that a short to ground could have blown some other fuse or what ever electronic module combines the vehicle's separate right side brake and turn signal lines into one line? If so, where would I find them on the vehicle?

[JohnWill]

It's quite possible that a fuse or the diode module that combines the lights took a hit if the line was shorted. I've build the module to combine them, all it consists of is some diodes.

[cwwozniak]

At first I thought it was just some diodes as well but the behavior of the still working left trailer light looks like it may be more complicated. The light blinks when the turn signal comes on and burns steady when just the brakes are applied. However, it blinks when both the turn signal is on and the brakes are applied. I don't think you can get that ability with just diodes feeding from the wiring for the separate brake light and turn signal lights in the vehicle.

[JohnWill]

Thinking about it, you're right. I'll have to find that schematic, I did that 20 years ago. Nowadays, you can buy them for $10 or less, so it's not worth the effort. I must have had an XOR in there for the lights. I must have had some of the old TO-3 power transistors in there as well. Now I'm curious what it was actually wired like...

[cwwozniak]

I am more curious as to where the OEM module to do that is located on the Yukon and what it looks like. The owner is going to take the Yukon back to the dealer and see if the problem is covered by the warranty.

EDIT: I did come up with a circuit that uses three SPDT BOSCH automotive relays and a couple of diodes (add three more diodes if you want snubbers on the relays).

[Who's Me]

You say you get no power at Right brake/turn contact. That is fed by dark green wire. that wire comes from fuse 6 (10A) in the underhood fuse panel which is switched on by TRLR RT stop/turn relay, also in that panel. that relay is triggered by the Body control module (Behind lower left side of dash)
That is if my wiring diagrams are correct. They've been wrong before.
Hope this helps.

[K7M]

Who's me is correct in saying there is a fuse for the turn signal. Your best bet is go to the owners manual for their location.( I believe he is correct on that also) All factory wired vehicles have separate fuses for all the connections in the trailer plug. Gm color code for their trailer wiring is as follows. blue is for electric brakes. black is 12 volt to charge trailer battery. yellow is left turn/brake. brown is tail lights. dark green is right turn/brake. white is ground. light green is back up lights.

[cwwozniak]

Originally Posted by Who's Me

... wire comes from fuse 6 (10A) in the underhood fuse panel which is switched on by TRLR RT stop/turn relay, also in that panel. that relay is triggered by the Body control module (Behind lower left side of dash)

Originally Posted by K7M

All factory wired vehicles have separate fuses for all the connections in the trailer plug.

Thank you both very much. I found the fuse panel on the side of the dash and I did check the right turn/brake fuse there. I did not know of the second fuse panel under the hood and the trailer connector having its own fuses. I will be checking the fuses there tomorrow morning.

[cwwozniak]

Problem solved. Fuse #6 was blown. Replaced it with a spare 10 amp fuse from the dash fuse box cover and the lights are all working now. Told the owner they should probably get themselves a small box of assorted fuses to keep in the vehicle.

Thank you again.

[JohnWill]

Probably as a result of those burn marks on the wiring.

[Who's Me]

JohnWiil is most likely correct on those burn marks.
I would probably cut out the damaged section and reconnect it with something like this,
http://www.wiringproducts.com/contents/en-us/d492.html
The heat shrink version will help keep moisture/road salt from corroding the wire from the inside. you can get them from most auto parts/marine stores.