I have the same problem on my 06 megacab but on the right blinker. Running lights work but no brake and indicator. I figured out that its coming from the box that is on the driver side under the hood. Dont know the name at this moment. Its a bad dial on the board.

 

That blows and would actually explain why there was a splice from the blinker wire on the rear tail light, to the wire to the trailer plug. Whoever wired my third brake light shorted something out or found out there was a problem, thought they did it and tried to "fix" it. Sounds like a 3 to 2 converter or whatever it is, is what I need. I don't care, I can splice that in no problem. Where would I get that?

 

nevermind. ebay, trailer shop, i can deal with that.

 

here's something I just thought of. Parking lights DO work on that side. What does that tell ya? separate wire?

 

did you ever buy a tester? They are cheap, I got mine at Uhaul lol

 

Yes the running lights are a diffrent relay,fues and wire.
The Left turn/Barake has its own relay, fues and wire.
The Right turn/Brake also has its own relay, fues and wire.

 

I fixed it last night. I got a hold of the 2600 page service manual a few weeks ago and looked at all of the different circuits and fuses involved. It is amazing how much wiring is in these trucks. I turned in the flashers and opened the fuse box, I could hear the relay clicking away for the flashers. The second fuse I checked (number 43) was blown. I replaced the fuse and whammo! the second flasher for the emergency lights started clicking away. I plugged in my tester and everything was working perfect. i spent 2 nights lying under the truck chasing wires and the real issue was a simple fuse.
Check the fuses. 30 33 43 and 44 I think are the fuses related to the trailer plug.

I wish I had started in the front first. Now i know better next time. Also see if you can get your hands on the 2600 page service manual. It has every detail and bit of information on our trucks.

Joe

 

Interesting, Joe. I'll check them out when I get home tonight. I think I managed to check out two fuses, but didn't know there were more to check. I may even go as far as popping the module out and seeing if maybe there's just a bad connection in there somewhere.

 

Well, my fuses are a little different. I think 46 and 47 for the trailer brake/signal lights on mine. Both are good. The other two are for trailer parking lamps and something else, I forget, but both of them were good. Not 30 and 33, though. Looks like I'm back to my original plan, patch in the 3 to 2 wire converter and call it a day.

 

Mine turned out to be a very easy fix. Pulled the 7 pin harness from my bumper, disconnected the plug, gave it a shot of contact cleaner and some dialectric grease.

Put it all back together and all is well.