I have a 2003 that has the seven pin socket as well as a 4 pin that's just underneath in the rear. Suddenly, my left turn and brake lights don't work. Took the socket off and cleaned it all. The socket has good continuity from the large blades to the pins where it plugs in. I get no power for the left at the seven pin plug, nor the 4 pin plug. Lights on the truck itself are fine, and all the fuses are good. Any idea where to look next?

 

Check at where the trailer harness hits the rear wiring.

 

I just fixed this problem on my 04. It is most likely the relay embedded in the pcm (fuse box). The fix is to take the fuse box completely apart and des older the relay and solder a new one in. My left turn relay was broken inside. I'm still furious at dodge for this design. A plug in relay would be a 30 second fix.
I have some of the zettler 30 amp relays to do the repair that I will sell if you need them. They are tough to find. The alternative is to replace the fuse box if the relay is the problem. Good luck.

 

Prione, is there a way to check that to see if it's actually the problem? And to be clear. Yours was the same thing exactly, with everything working except no power to that one pin?

 

Train,
Yes, everything but left turn/stop on the trailer worked. I checked continuity from the 7 pin connector to the c1 plug on the fuse box (yellow wire) to make sure the wire wasn't broken. That leaves the relay or the forward control module (silver box on the fuse box. If you hear the relay clicking inside the fuse box while signaling left turn then it has to be the relay contact. The contact inside mine was broken off so it sounded different than right turn (boing instead of click). If the relay doesn't click it could still be the relay coil OR the fcm not triggering the relay. The Tyco relays are crap so the contacts can break easily. I tested my relays with an ohm meter and a 12 volt power source to find the bad one since they are marked relay 2,3 and 4 not right,left. I'm an automation controls engineer so testing this stuff makes sense to me. I realize that it can be mysterious to folks that don't work on this type stuff. I hope I explained it well enough. Let me know if you need more info.
Prione
P.S. I would like to horse whip the engineer that came up with putting the trailer light relays on the circuit board INSIDE the fuse box. What a jackass! There are spare sockets with the other relays that could have been used.

 

Did you replace all three or just the one? If one, can you try to explain which one? I found and excellent video on this, but he just went ahead and replaced all three relays.

 

I think the left turn is relay 3. It was the one closest to the edge of the circuit board. I replaced all three since one broke the others may be close behind and it's a real pain to get to them. I wasn't able to find anywhere to buy them one at a time either. I had to buy a bunch of them to meet the minimum order that they would sell. That's why I have some to sell. A new fuse box is around $500.00 from dodge.

 

I found another case of someone needing to be horse whipped.

Decided to check the wires first just in case it was something else like HeyYou suggested. Went from the pins on the back end, to the slots on the TIPM plug. NOTHING! Well crap. How could anything break or get chewed as it's all encased in loom? Look. Look some more. Keep looking. All this being done on a creeper of course. Finally notice the plug right behind the drivers wheel well. Amazingly, you can see the proper wire right on one corner of the plug coming from the back end. Start wiping off dirt to see if the connection is good. Well guess what? The wires coming out of the other side and going to the TIPM............ CHANGE COLOR!!! Can someone explain the reasoning behind something so stupid?

 

Prione, sent you a PM.