No left turn signal or brake light on trailer,checked all fuses they were fine I had no power at the plug in at the back of truck on the left side for brake light or turn signal the running lights are working fine?Thanks very much!

If the trucks left side works, then it is a wiring problem. If it works at the plug(test light) then the trailer light has a bad ground. If it doesn't work at the plug, then it is a bad power wire from the turn signal wire to the plug. Some times it is the plug itself. Truck or trailer. Corrosion.

Try the specified fuses in the under hood fuse center. they are common to blow.

Try cleaning the fuse contacts, it may not work but is worth a try. I used an ignition breaker points file that i ground a bit off one side so it would fit in the contact slots when the left turn signal and brake light wouldn't work and it was successful on my 2009 grand caravan. I didn't know there was a problem until i hooked up the trailer and saw it had no left brake/stop lights. I used a small test indicator that plugs into the trailer connector and has 4 leds which light up when each item is activated. use a trailer connector kit that has the male and female connector connected to a 4 foot long wire set I bought at Walmart. I plug it into the car connector with the test indicator plugged in the other end and held on the rear window by the wiper blade so i can see in the rear view mirror if all the lights work. For a sedan I put in on the ground, anchored by any tool handy, so i can see it in the side mirror. It beats running back and forth to see if I made a repair.

Standard wiring colors are as follows:

4-Way

5-Way

6-Way

7-Way

Green

Yellow

Brown

White

Red

Blue

Purple

Right Turn & Brake

Left Turn & Brake

Tail Lights

Ground

Backup Lights

Electric Brakes

Auxiliary Power
Green- Right Turn and Brake
Yellow- Left Turn and Brake
Brown- Tail Lights
White- Ground
Red- Reverse (Back Up) Lights
Blue- Electric Brakes
Purple- Auxiliary Power

It sounds like your green and yello wires are shorted together somewhere along the length of the harness. I would check the wires on the trailer first. Easier yet, if you have another trailer to connec or access to another to use for testing, connect to it and see if the problem repeats; if it does the trouble is in the vehicle's wiring.

Well let me shed some light on this issue. I have the same problem. Trailer connection from truck does not have power to left turn signal and left brake light. I just got back from the dealership and $100.00 labor charge. My problem is the TIPM (Fuse Box for short) and FCM (little silver module hooked to the Fuse Box on the left hand side of the fuse box). $910.00 for the parts and Chrysler doesn't have any in stock. 4-6 weeks to maybe fill a back order. I am currently researching an alternative way to fix this issue. I will let you know.

I lost the light in the 2003 Duramax a few week ago.I just found a blown fuse under the hood in that big fuse panel by the driver side. It was the 15 amp mini fuse on the upper left hand corner. There was a white arrow pointing to it. Evidently someone has had the problem before. I bet that's my culprit

Check the lug on the truck to be sure it doesn't move when the plug is connected. I had one that read 12 volts when I tested it but would slide in or move when I plugged into it. I replaced the plug on the truck and it solved that problem. Trailer wiring typical is yellow to the left turn/brake light. Does the left brake light work? Do the flashers work? Double check the fuses also... to left turn/brake on trailer. Hope this helps. Mike

I have the exact same issue. I have also tested my trailer on other vehicles and it works fine. I even purchased a light up tester and found the problem at the harness. It seems like a bad ground to me but I can't seem to find one.

The trailer lights have a common brake/turn wire while the truck has seperate turn and brake lights. I think the problem lies with the device that marries the two for the trailer wiring but I don't know where to find it?

you prob got a trailer plug prob bad wires if not tail lights run through turn signal switch tell fix ya bout me ok

if your vehicle lights are working all the fuses will be good. follow the cable from the towing socket on your vehicle , it will most likely go behind one of the rear lights to connect into your cars system,
check your tester where the cables join and you should find the problem. hope this helps.