For decades, hooking up trailer lights and electric brakes on most cars meant splicing into the wiring harness near the back bumper and just adding the extra load of trailer lights and brakes to the car’s electrical system.
However, today’s vehicles are refined to the point that adding a few extra lights can cause fuses to blow, wires to melt, and possibly even lead to total electrical failure.
My own experience had me frying the wiring going to the car’s brake light switch like it was a light duty fuse. I should have heeded my own concern when I realized the size of the wire was considerably lighter than the wires used in cars manufactured years ago.
You can avoid having a similar meltdown by removing the load of the trailer wiring from the car’s electrical system with an electric brake controller.
Here’s how I wired an electric brake controller on 2 different vehicles…
Step One: How To Wire The Trailer Lights
Today there is no reason to ever cut, strip, or harm in anyway the original wiring harness on most cars.
Aftermarket plug and play wiring harnesses are available that allow you to simply unplug the connector at the car’s taillight assembly and plug in the new harness between the taillight and the car’s original wiring harness.
Here is an example of such a trailer light wiring kit available online.
It’s very important that you use such a kit — because, in many cases, it will hook directly to the car’s battery. This removes the added load of the trailer lights from the car’s delicate electrical system.
It’s also very important that you purchase a wiring kit specific to your vehicle. These are not one-size-fits-all, and the wrong kit may damage your vehicle.
Step Two: How To Wire The Trailer Brakes
This is where it gets a bit tricky.
It was while hooking up an aftermarket brake controller that I fried the wiring on my Dodge Caravan.
That’s why the absolute best idea is to choose a vehicle that came from the factory with a trailer towing package.
The brake controller wasn’t there, but the wiring from the brake switch to the trailer plug was already in place. Hooking up the brake controller was pretty straightforward with the standard wiring harness that comes with the controller.
This brake controller wiring diagram shows which wire goes where.
Getting back to the Dodge Caravan… it didn’t come with the factory tow package, so I had to start from scratch.
The best deal locally was purchasing a hitch from U-Haul.
Installation was simple and required no drilling or special tools. As mentioned earlier, the trailer light wiring kit was purchased online and also was simple and straightforward to install.
The brake controller needed only one minor alteration to remove the additional load from the car’s electrical system.
Referring back to the brake controller wiring diagram, all connections are made directly to the car’s battery. Except for one: the wire going to the car’s brake switch! That’s the one that caused the wiring harness to melt down on my Dodge Caravan.
Instead of hooking it to the brake switch, you can run that red wire to a dash mounted push button switch and continue from the switch back to the + Pos battery connection at the inline fuse.
This will remove any chance that you will cause damage to your car’s original wiring. Do understand though that your trailer brakes will only operate when you push this new dash mounted button.
Again, your trailer brakes will NOT engage if you push down on the car’s brake pedal!
This is a way to avoid damaging your car’s electrical system.
Is it the best way? No. Purchasing a vehicle with a tow package in place is always the best choice. This is simply a way to work around some of today’s load sensitive cars that can’t handle the added electrical draw that trailer hookups require.
I’ve been involved in RVing for over 50 years — including camping, building, repairing, and even selling RVs and motorhomes. I’ve owned, used, and repaired almost every class and style of RV ever made. I do all of my own repair work. My other interests include cooking, living with an aging dog, and dealing with diabetic issues. If you can combine a grease monkey with a computer geek, throw in a touch of information nut and organization freak, combined with a little bit of storyteller… you’ve got a good idea of who I am. To date, I've shared my RV knowledge in over 300 articles here at The Fun Times Guide!