Right Rear turn signal bulb on ALL the time, right front blinks fast

[GBergen]

Others have said it "love the truck, hate the electrical!"
It was about a week ago, I walked up to the rear of my 2004 and found the right rear turn signal burning brightly. The keys were in my pocket, the rest of the lights were out. When I used the right turn signal, the right front would flash fast but no change in the brightness in the right rear turn signal. I still have standard bulbs in the truck, no LEDs .
I pulled the left tail light assembly and swapped it with the right one, same thing, right turn signal burning brightly.
I removed the right turn signal bulb to keep from draining the battery during the evenings, but I hate to travel without turn signals on one side.
I've looked through the schematics for the turn signal paths, and much of my troubleshooting is pointing to the FCM.
I'm nearly certain (but that's why I'm asking for help) that the PDC is not the issue... While trying to solve a front left headlight issue last year (but that's a different thread), I had the PDC apart and have a ton of pictures of whats inside if anyone would like to see a relatively pristine circuit board because that's all the PDC appears to be aside from the soldered on relays for the trailer turn signals on it, and connections for fuses/relays. Oh, I had to bypass those trailer turn signal relays a couple of years ago, due to the one that controls the right rear trailer turn signal to stay on all the time as well but that's a different thread.

If I read the schematic correctly, the FCM sends a hot and not a ground to make the bulb flash. Let me know if I missed something there.
I'm suspecting the FCM is somehow sending the wrong information out, telling the system (itself?) that there is a bulb out in the right turn signal side, causing the right front to flash fast and at the same time turning the right rear turn bulb on and leaving it on.
I'm hunting for ideas for things to check before I spring for a new FCM. Have I overlooked something obvious?
Thanks for your help!
GF

 

[PWong]

I would like to try a new socket board first before FCM.

 

[mwilson]

If you live where winter road chemicals are used check the trailer lighting socket for green stuff.

 

[DaveHess]

GBergen, I would love to see how you modified the inside of the PDC. I bought and installed a new PDC for my 2003 and that fixed my trailer turn signal problems. I kept the old PDC and was able to source new relays for the three relays on the bottom of the circuit card. What I don't know how to do is to remove the rubbery film from the board to desolder the old relays. Do you have any suggestions? Sorry to hijack this thread!

Dave

 

[GBergen]

thanks for the tips!

PWong,> I exchanged the left turn signal socket board with the right one. Both boards work when connected to the left side of the truck. both fail when connected to the right side.

MWilson > It has recently become quite crappy on the roads here. I'm going to check this as soon as I can get someplace out of the snow to check the trailer connector.

DaveHess > I replied to you in a PM.

I'll keep trying to resolve this. Thanks for the reply's.

 

[GBergen]

Hmmm. I've checked both the flat 4 and the round 7 trailer plugs and get a similar reading, that the right turn signal is on. No CRAP shorting within the plugs. I can't say that I understand why there is 5V on the left turn signal lug and 3 V on the park light lug of the trailer connector... Very strange. So I'm nearly convinced that the Forward Control Module (FCM) is sending the wrong signals to the rear bulbs. The weather has been too crappy to do any crawling around under the truck looking for gremlins in the wiring. Has anyone purchased an FCM for a reasonable cost? This is the part number on the PDC is P56051038AC A and the FCM is 56051036AD A date code is 19003. Thanks for your time in replying!
GFBergen

 

[mwilson]

I'm really concerned anytime that a rear light stays remains lit on a vehicle equipped with a towing package. A lot of people don't consider that there is a live trailer feed in that harness.

Now where you mention partial voltage on another pin I really suspect a green gooey mess in a connector or a pinched harness. Can you kill that trailer feed up front and see if the light goes out?? Maybe a fuse that can be pulled??

 

[mwilson]

Not saying it couldn't be the FCM, just do a little more free troubleshooting first.....

 

[BigPapa]

A lot of people don't consider that there is a live trailer feed in that harness.

I once had my brake lights staying on all the time on my '95 2500. I looked EVERYWHERE and came up with nothing. I finally pulled my trailer connector apart and found ONE STRAND of wire from the live trailer feed was touching the brake light wire connection.

 

[GBergen]

Thanks for the reply,
I'll get some contact cleaner and spray out the trailer connector(s). I saw dielectric grease in there but wasn't too worried because its non-conductive, BUT it was dark and the lighting wasn't great to see way in there. The bizarre part is that the FCM flashes the right front bulb real fast so it thinks there is a bulb out somewhere at the same time the right rear is on steady.
It's been crappy cold and slushy here for a bit, so I'll need to find a warm spot to continue the investigation.

Big Papa, while I'm cleaning the connectors, I'll have a look for stray wires.

IF it comes to buying a new FCM, any recommendations for where to find them inexpensively? I see a couple of web sites that want $200 (or more) + a core charge of $125. What the heck do the want a core charge for? I've not seen ANY refurbished ones and I wouldn't buy them if I did find them.
Thanks for your time in replying.

 

[BigPapa]

You'll have to take the connector apart to see where the wires connect to the connector to see what I found. I have no idea how that happened on mine. It's inside the housing, covered, and there's no tension on the wiring. Freaky.....

 

[GBergen]

solution?

I finally found a warm spot to do some additional troubleshooting. I used some contact cleaner in both the flat 4 and 7 pin trailer connectors. I noted that the odd voltage on the driver side turn/brake pin in the trailer connector (about a volt) dropped a little after the cleaning. It may have been caused by some "KOPR-SHIELD" (made by Thomas & Betts for electrical conductor protection) that got slopped between pins in the trailer socket and created a conductive path.
In November of 2010, I installed a NAPA power convertor (part number 755-1841) to bypass the relays on the bottom of the PDC for the trailer turn and brake light control. At the time, I wasn't willing to take the PDC apart to replace those relays, but I've disassembled the PDC for other reasons since then. The NAPA power convertor had a 90 day warranty. It has an independent power connection from the battery to power the convertor and send power to the trailer turn, running and brake bulbs when a electrical signals come from the truck system. I'm still working on the verification however, when I disconnect the independent DC + to the power convertor, all passenger side turn signals return to normal operation. All three bulbs in the 2004 RAM tail light use the same bulb, so I pulled the back up bulb and put it into the turn/running light socket and drove home. I'm strongly suspecting this after market part from NAPA as the cause of my frustration, because when I put the fuse back in, the right turn signal bulb lit up again solid with the truck off and keys out.
Thanks to all who contributed

 

[BigPapa]

NAPA power convertor

This could very well be your issue, not that it's NAPA brand, just the "converter" part. I have seen them fail and cause a similar issue. I would disconnect it and see how it goes.