I am having the same problem. Did you ever get an answer to this problem?

 

all you do is turn the *** on the top of the fuse box and the lid comes off easily

 

Sorry you all I had same problem. It is in the PCM.

 

you need to read MDinger's post again. He's got the right T-shooting. If the truck works fine without the trailer hooked up, then the prob is in the TRAILER. Chec k the resistance, not the Voltage on the trailer. Check the wires on the trailer, like ya did with the truck

 

My 2006 Ram 2500 also is experiencing problems with the trailer lights. The lights work fine on the truck and when I hook up a trailer the running lights and license plate illumination on the trailer work but the turn signals, stop light and hazards do not, however, the lights continue to work as they should on the truck. I looked for a short in the harness or a short to ground with no luck. I have identified this fault with three different trailers.

 

If the problem was on the trailer then the truck side of the trailer wire harness would have voltage for both the right and left side signals. The fact that he doesn't means the problem is truck side and NOT trailer side.

I'm also having the same problem but I think mine is a loose connection right at the bumper because I had no power but when I reach behind and move the harness around I can get everything but the left side.

fredsr55, out of curiosity for a worst case scenario how much did it cost you to replace your PCM?

 

i work at a trailer place in texas. if you take it to any major trailer repair place the will have testers that they can hook up to the truck and the trailer which will tell you if the problem is in the truck or in the trailer, if they are like us they will do this for free. Second, the truck lights and your 4-way/7-way plug on your truck are on 2 diff systems, so your truck lights are still going to work even if your trailer light wiring on your truck has a short. Hope this helped.

 

From my experience and VERY similar sounding problem, Marx is 100% correct! There is a printed flex circuit thing under the relays/fuses that will get corroded. I tapped into my truck wiring with an in-line 20 amp fuse for the particular trailer lights. Haven't has 1 problem in over 2 years.

 

That's my plan if I can't get my harness to work.