Factory trailer wiring and relay!?

[morgankshaw]

Ok guys Ive been searching online and this website for answers or a wiring diagram to help figuring out the tow wiring on my 87 f350. I believe this is the factory tow harness.

There was a lot of bad and crazy wiring on this thing and I ripped out the funky old brake controller earlier this year and didn't take pics!

Anyway I have 3 wires entering the cab that I hope need to be connected to the brake controller.
Yellow/red, red, and blue/black

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This exits the cab and seems to merge into this connection

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Then it can be plugged into this harness which continues down the frame to a 7 way plug and the round connector at the end seems to plug back into my tail light harness.

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My question is about the first picture. Are the 3 wires inside the cab supposed to be connected to the brake controller???

Thanks for the help! I'm trying to get all my lights working and take my newly completed beast on its first camping trip. But I need lights and all that fun stuff to get legal and on the road!


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[Shawn MacAnanny]

I think brake controllers are usually 4 wires? Constant battery 30amp or so fused 10gauge, ground 10 gauge, brake pedal/light switch 12-14 gauge and trailer brake output 10gauge. I wouldn't reuse any harness your are positive of the condition on.

 

[morgankshaw]

Yes, thank you Shawn.

What I'm trying to find out though, is what are the functions of the first 3 wires I posted. I'm assuming the 4th wire from a brake controller will be a ground so that's why ford only supplies the 3.
I was hoping someone had a diagram or knew what each was.


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[chillman88]

On my 91, red with green stripe goes to the back harness. No clue why, it makes 8 wires so I never hooked it up. I presume it must be for the brake LIGHT output from controller. My controller is the old hydraulic line style, takes 12+ ground, brake light out, and trailer brake out.

My truck had blue (to trailer) and either red or black, don't remember but it was constant 12v+

Can't quite tell your wire colors.

 

[79jasper]

Personally I would take out anything aftermarket and start over.


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[morgankshaw]

Personally I would take out anything aftermarket and start over.


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I did. This is original


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[morgankshaw]

I'm getting a new towing relay and multifunction switch


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[79jasper]

Oh. Lol
Let's see if anything has a wiring diagram.

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[morgankshaw]

Oh. Lol
Let's see if anything has a wiring diagram.

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Yes I can't seem to find one for the optional factory tow harness. That's what's so frustrating.


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[chillman88]

I don't know if this will help, it's for an 86.

http://www.garysgaragemahal.com/trailer-option.html

 

[laserjock]

That red wire is probably the factory hot from the starter solenoid with fusible link. I want to say the blue/black is the trailer brake from the controller(further supported by the stub of blue wire in the butt splice. The third would make sense it's from the brake switch although my brake switch has a green wire with I believe red chaser on it. Best thing to do is just test them. Red should be hot all the time. Yel/red hot on brake pedal and blue should travel back to the trailer plug.

 

[morgankshaw]

That red wire is probably the factory hot from the starter solenoid with fusible link. I want to say the blue/black is the trailer brake from the controller(further supported by the stub of blue wire in the butt splice. The third would make sense it's from the brake switch although my brake switch has a green wire with I believe red chaser on it. Best thing to do is just test them. Red should be hot all the time. Yel/red hot on brake pedal and blue should travel back to the trailer plug.

Yeah it's frustrating because as of now my power probe detects nothing at all 3. But I'm installing a new blinker aka multifunction switch and I ordered the trailer harness relay and a multifunction relay even though I can't seem to find it? Hoping that livens things up and gives my non working blinkers and brake lights some life. If all else fails with the factory tow harness I can always wire my own but it's nice to get the original stuff to work.




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[morgankshaw]

I don't know if this will help, it's for an 86.

http://www.garysgaragemahal.com/trailer-option.html

Well not exactly the same but closest thing I've seen. Thanks!

I suppose I need to learn to check a fusible link while I'm at it. YouTube time!


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[OLDBULL8]

What make brake controller do you have?

https://www.etrailer.com/faq-installation-of-brake-controller-from-scratch.aspx

 

[morgankshaw]

What make brake controller do you have?

https://www.etrailer.com/faq-installation-of-brake-controller-from-scratch.aspx

It's a prodigy G3 or something like that. It's a newer one. Haven't opened the box.


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