Re-wiring factory trailer harness

[Ironforger]

Not sure If I'll need help with this topic just yet but decided to start this thread / discussion to help me get the mind-set. Maybe this thread can help others who need to sort out the trailer wiring.

Ok so when I bought my truck in 2013, it didn't have a bed or body on the back. I basically bought a truck with just a cab.  Previous owner was using it as welding rig. He got a new truck and swapped the welding body onto his new truck.  Unfortunately he was not so nice and he cut ALL of the wires in the back for the tail light and towing.  Left me with the rats nest bunch of cut wires.  I used a test light to get the basics connected for the stop, turn and tail lights and a basic 4 pin connector for a small utility trailer.

Now I'm getting ready to setup wiring correctly with an aftermarket 7 pin connector. I'm getting ready to do a little more serious towing.  I'll be towing a 10,000 lbs dual axle / electric brakes enclosed car trailer from New Jersey to Florida Multiple times this May and June, each trip 2000 miles round trip.. 

I appreciate the availability of the 2002 FSM from the mopar1973man website and found the wiring - trailer tow diagrams.  This will help with identifying the wires based on color codes among the mess of cut wires.

This truck has the factory trailer tow package. There is a trailer relay in the PDC.  There is a brake controller under the dash which appears to be wired to and connected to the factory harness, plugged above/in front of the brake/clutch pedals.  The brake controller appears dead, and upon brief investigating found a blown trailer Jcase fuses in the PDC. (Mine had a 20 amp Jcase in the trailer slot, it should be 40 amp. Also, the stop lamp had a 40amp Jcase it should be 20 amp. I'm guessing the previous guy swapped them for some unknown reason. Also, for some reason the fuse slot numbers in my PDC don't match the fuse numbers in the FSM trailer wiring diagram. Is this a common issue? Wondering if it's a typo in the FSM.

Going to try to figure out these cut wires one day this week, hoping for nice weather.  For starters I've at least identified the LB (Light blue) electric brake wire among the rats nest.

 

Pictures below starting with the rats nest:

 

 

 

 

 

 

 

The brake controller, factory or dealer installed?

 

MY pdc. Jcase fuses are mixed up.  

 

FSM Trailer Tow wiring diagrams:

Edited April 19, 2020 by Ironforger
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[Towrigdually]

For the mess of wires I think the easiest route would be to go to the junkyard and cut off the wiring from just behind the fuel tank and back, then splice onto your truck and not worry. 
 

if that’s not an option, the. I’d start by taking every single piece of wiring off that truck that doesn’t look factory. Then find what you need for running/tail light. Take what’s left and if they are needed for a 7 plug then keep it not cut away. 
 

as for the relay and fuse problem. I’m running the same in mine as written on the pdc cover and never had an issue. So the FSM could be wrong but who knows. 

Edited April 20, 2020 by Towrigdually

[Ironforger]

Thanks @towrigdually,

 

Great idea although not sure if I'll  have time to hit a junkyard.

 

I'm considering a hopkins connector as well:  https://www.carid.com/hopkins/endurance-7-rv-blade-molded-car-end-connector-with-cable-mpn-20022.html  I'm customizing my service body step bumper - recessing the vehicle side 7 blade connector so there's less chance of breaking it while I'm not towing.

 

Glad to hear your pdc fuses have the same config.

 

How do you like that current tune you are running? pm sent

 

 

[Towrigdually]

That Hopkins connector is solid, I have it on my 1500, I should went with the one that had a flat 4 plug on the side also so I didn’t need to carry an adapter, but that’s just me. 
If your able to salvage your factory wiring and female wire end, this could be an option for you since it’ll be plug n play. 
 Hopkins 42145 Plug-In Simple  Multitow 7:4 OE Replacement Harness https://www.amazon.com/dp/B000CMHVF8/ref=cm_sw_r_cp_api_i_A8CNEbKG1E1A6

 

as for the tune, the XZT is good I like it, simple and easy. I have the high idle mode on it also so that’s nice in the summer when I leave the dog in the truck. Also great in the winter for warmup.  
you can get the tunes and how to adjust what version you’d like on it here on the website. Just take alil time on the computer.