Dodge Cummins Diesel Forum banner

1 - 20 of 27 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter #1
I’ve tried to understand how this is happening with no luck. Not sure if this is the right place but I’ll give it a try.

Trailer brakes work fine, running lights work fine (both sides), right side brake and turn signal work fine (truck and trailer). Left side brake and turn signal don’t do anything On trailer but truck is fine.

I have measured voltage at the truck trailer plug (left and right) with running lights on and getting about 9 volts. Push brake or turn signal on left side and get small increase (~9.5 to 10 volts) on plug, right side is about 11 volts). When I turn the running lights off the voltage on left side drops to 5 volts. Not enough to get LED lights on trailer to go On for brake or turn signal. Verified with power supply the lights on trailer are fine.

do I need a new plug and harness for truck? I’m baffled by this thing.
 

·
Registered
Joined
·
6 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter #3
Thanks for the reply, to confirm yours was also not transferring the brake and turn signals but the parking light function was working? And this solved the issue?

I have found some threads that showed the relay issue with the fuse block. Since I have some voltage coming across the terminal at the back of the truck I don’t think this is the issue. Considering the cost of replacing that, I am all for easier fixes. The other thing I was thinking is running a jumper wire from the brake light down to the pigtail.
 

·
Trying to learn
Joined
·
5,861 Posts

·
Premium Member
Joined
·
5,704 Posts
Yep, would try with incandescent test light, some circuits in IPM needs to see load, Should be 12 volts, could be led/resistance issue.

Connecting directly to taillight can damage that circuit, would need relay to avoid issue.
 

·
Registered
Joined
·
72 Posts
I would start with testing the wiring at the back of the socket, look for where any splicing may have been done.
Get you a copy of the FSM and be sure you have the proper power to start with before replacing parts.
FSM → Newbies guide to your new to you truck

There are many lower-cost options for replacement sockets.
I had the same problem. Turned out it was a poorly done repair. Looks like the wire had broken and the previous owner tried to splice and solder. It worked for a while, but the solder joint was crap and it was pulling apart and only making a partial connection. In my case the splice was about a foot and a half from the socket. It was easy to see since there was a lot of newer(ish) electrical tape.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #7
Thanks everyone, didn’t have a chance to get under truck tonight but will look tomorrow and do some testing. I’m starting to think there is something in wiring. I found a fifth wheel/gooseneck trailer plug hiding behind the bed liner. Looks like someone just cut the second adapter out of the harness, I have no idea why you would do that and not just leave it hooked up.
 

·
Registered
Joined
·
6 Posts
I should have elaborated more.... I found what I felt was a loose pin in the connector, so I replaced the plug.

During the replacement of the plug, I found some butt connectors in the trailer harness. So I elected to replace the pig tail.

so as others have suggested, check for poor repairs from previous owners.

hope you can fix it cheaply

-jason
 

·
Registered
Joined
·
16 Posts
Discussion Starter #9
I found where the harness was spliced to add a gooseneck plug in the bed. Fixed the yellow and pink wire, lots of corrosion and pulled apart without any effort. I now have no left turn or brake light on truck, no brakes on trailer, no brake or turn on right of trailer but have on truck. Lamp out is on dash but bulbs are fine. Ordered replacement pigtail and will solder and seal new connections. Hoping this doesn’t end up being issue with power block like I’ve read is an issue on these trucks.
 

·
Trying to learn
Joined
·
5,861 Posts
What year is your truck?
Seems like the wiring to the left side is incorrect.
Use a test light to find wires from the front at the back, test each for function.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #11
It’s a 2003, I used a test light prior to fixing the repaired area and found yellow with pink stripe to be left turn/brake for trailer.
 

·
Premium Member
Joined
·
5,704 Posts
Test for good ground on truck for left/turn stop light ?
Check for good power from relay for trailer in PDC, never going to work if PDC relay is bad.
PDC relays are fixable/upgradable with basic soldering see
 

·
Trying to learn
Joined
·
5,861 Posts
The truck light circuit and the trailer lights are different.
Did you DL the FSM? it will show what wires to look for.
 
  • Like
Reactions: rghavana

·
Registered
Joined
·
6 Posts
good find on the poor splice job

but back up a moment. Have you checked all the fuses? Could've popped something doing the repair.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #15
Being the wiring is separate that’s why I’m even more confused. I purchased a new pigtail and it will be here Monday afternoon, I’m going to undo all of beautiful tape on the harness and start diagnosing.

I did download the FSM, that’s a huge help. Thanks for the link.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #17
Thanks again for all of the help!

Looking at FSM, trying to figure out all of the wire colors for harness. Here is what I have and what I am missing:

Parking - Black/Orange
Left Turn - Yellow/Pink
Right Turn - White/Pink
Electric Brakes - Dark Green/Black
Backup Light - Violet/Black
+12 - White/Red

Missing the Ground? Plain Black?

Please correct as needed, rain rolled in so not going to work on it tonight.
 

·
Trying to learn
Joined
·
5,861 Posts
This is how I wire mine. colors are different 'tho.
Sorry wrong pic.
Correct pic for Dodge.
 
  • Like
Reactions: rghavana

·
Registered
Joined
·
16 Posts
Discussion Starter #19
thanks, should have been more specific. Looking for the wire pigtail colors on the truck, FSM makes it less than clear with factory tow vs add on.
 

·
Trying to learn
Joined
·
5,861 Posts
8w-52-4
Left rear of the truck:
Turn = DG/RD
Stop = WT/LG
 
  • Like
Reactions: rghavana
1 - 20 of 27 Posts
Top