I have a 1986 F250 Diesel that I have been working on setting up as a tow vehicle, fixing lots of issues, getting it into good shape, etc. I've come to the point where I am looking at the wiring for the trailer connector and brake controller. The current trailer connector wiring is, frankly, a rat's nest. I want to tear this all out and replace is with a clean install that I know is done right. At the same time I am replacing the trailer brake controller with a Tekonsha P3 (the old one was making a funny noise).

So basically I am redoing all of the wiring related to towing. I'm wondering if anyone knows of guides for best practices, has advice or other helpful tidbits as I start on this project.

What I am currently thinking I will do is remove all the existing wiring and replace with sheathed seven conductor wire run to the cab (12 & 10 gauge for the new wire, the existing wire is all separate wires just stuffed into places). I will then make all the connections in the cab of the truck where things are more protected to start with and I will also solder/shrink wrap all connections. I will of course remove the old wiring and repair the places where power taps were installed onto the brake lights and such (cut and solder the wires and then seal with heat shrink tubing). I'm hoping that this will make for a very clean and dependable installation.

Any thoughts/advice?

 

Sounds like you're trying to replicate a factory wiring harness and I don't see anything wrong with that - however, it will be a bit of work - but you've already acknowledged that as well...

There are no guides that I'm aware of that will show you how to do what you want to do. Literally every trailerr wiring harness I've seen in the aftermarket leverage the rear harness for the lights and use a "T" connector to be inserted into the factory tail/brake light harness. Trailer brake wiring has generally always been a single hot wire run from the controller in the cab, back to the female trailer receptical..

I think 10g is a bit on the large size for lights, but as long as you're going all the way - no harm. Using properly sized convoluted wiring sheath (tubing) I would go through the firewall and along the left side frame-rail. I would zip-tie every 10-12" to the brake lines, then up and over the rear axle hump on the frame - follow that back on the inside of the frame channel to the rear bumper mount. From there, you just need to finish routing to your receptical.

So - no best practices here. No fancy relays or anything like that. Just common sense.

 

Yeah, this is the wire I ordered: Deka Wire - Jacketed 7-Wire - per Foot Deka Accessories and Parts DW04914-1

Only the ground wire is 10ga, the rest (including the brake actuation) is 12ga. According to wikipedia, this is at or better than spec for all the wiring for a 7 pin flat connector. Essentially I want to put the time in on the front end and know that the wiring for the trailer will be completely reliable and that I won't have the wiring cut out when I drive through a puddle or some crap like that (the current setup very well might just short out on the frame in a couple of places just being jostled around).

When it comes to safety related items I take things very, very seriously/carefully. I want a unique tow vehicle (hence putting alot of time and money into fixing up a 1986 instead of buying something newer) but I am going to make it at least as good as a more modern vehicle would be.

 

I hear you and I don't like worrying about stuff like that either..
But I have to say that I have yet to have one of these fail on me...
Ford F-150, F-250, F-350 Trailer Wiring - 1986 | etrailer.com

 

BTW, one of my favorite trucks was my 84 F250 Supercab with 6.9 IHC diesel... Wouldn't win any races while towing, but had enough torque to get the job done without hurting itself or anything else in the driveline...

 

You might want to look at a current wiring diagram with the trailer connectors going through the engine fuse box.
I don't see where you discussed fuse links or a dedicated fuse box but definitely a necessity.

 

Yeah, I am working on figuring that part out. I'm thinking I will do a fuse & relay box for all the trailer connections. I will also put a headlamp relay into that same box. I'm currently spec'ing out if there are any other electrical upgrades that I need to make (wiring or otherwise, maybe a 3G alternator, etc.).

 

Here is what I did on my 90 F350, I used a relay for the driving lamp circut and then two relays that handled each side for turn and brake. Also after my first trip I upgraded the Alt. as the stock alternator was pretty weak once the trailer was lit up and you applied the brakes the voltage would drop enough to dim the lights. I did the same thing as you and made my own harness from the cab to the trailer connector, Only Diff is I also had legs that went for the Camper plug in and then also another one for when I hook a 5er up.

When I did this I also put a heavy duty Flasher relay in and the Fuseblock/ Relay panel I made has its own power feed from the Battery.

I over built my Trailer wiring because I often will have a camper in the back of the truck along with my enclosed car hauler and both of these have so many marker lamps I could drive with the headlamps off. (The Marker lamps were installed by a previous owner who said he could never see the trailer)

I got all my stuff from picowiring.com they are out of Eugene OR and have local dealers right down the street from my shop.

 

Nice sounding setup. Also, thanks for the link to the site, those kinds of sites are very helpful!