I just got my trailer brake controller installed and need to figure out how to wire my trailer brakes from the trailer plug in. I originally had a 4 pin so I didn't have all the wires back there. Are the wires already going from the cab back to that plug by the spare? Can I just hook it up to there?

 

No. You need the blue wire (usually 12ga.) run from the engine compartment to the rear for the trailer brakes. It will be fused or relayed for safety and power requirements. I'm listing a schematic to help you with your wiring. Good luck.

 

If you are installing a trailer brake controller use this schematic for wiring the controller. It's from Voyager. A well known brand in the industry.

 

I know it's the blue one but where do I run it to in the engine compartment? My controller has a harness I just plugged into the connector under my dash for it.

 

You should have the wires already run, when you look at the connector next to the spare, does it have all of the wires there, or just 4? If they're all there, you just need to put a couple fuses and relays in the fuse box and you should be all set.

 

Etrailer.com sells a harness for trucks with factory 4 pin plugs. It plugs in at the harness near the spare tire. It has wire that runs from there to the rear with a 7 pin connector that your trailer will plug into. It also has a pigtail for the plug by the spare to plug your factory 4 pin wiring back in so you will have both 7 and 4 pin plugs at the bumper. The kit also includes all of the fuses and relays to send power through for the additional pins. It's $60. Another member found the same kit on amazon for a little less. It is my understanding that all of our trucks have 7 pin wiring in place to the plug by the spare. Some came with the wiring that ran to a 7 pin at the bumper and some with wiring for a 4 pin. Those that came with 4 pin plugs just need the wiring from the plug by the spare to a 7 pin at the bumper and the relays and fuses to send power through the additional wires that are already in place. This kit should have everything you need. The site also has a video of the install. The best part is no splicing wires. The website explains it much better than I just did.

 

Look at the second schematic. It shows you where to hook up your controller wires. If you follow this pic you will have no problems with hooking up your unit.

 

Unless he has a factory or added trailer towing package, he won't have the extra wires run for the electric brakes. The factory towing harness has it inside the loom, but not a regular truck without.

 

So this is what I have: controller ha a harness I bought that connects into the plug under the dash (the brown and grey plugs in the upper left) so I cant just connect the wires like in the diagram without cutting wires off the harness. And I cant seem to trace where the stock plug wires are going under the dash there.

The connector by the spare has more than just 4 wires coming out of it. So I wonder if I cut the wire loom back there if some wires will be just lying loose back there?

 

This is some awesome information. Thanks for this! I'm just now putting in a controller for my RV. I was planning to splice in a bunch of wire but now I'm going to track down one of those kits you're referring to.