March 7, 2004
H2 Electric Trailer Brake Controller Installation
For some reason, auto companies decided long ago to leave electric trailer brakes up to the truck owner. Maybe its because there are different types of brake systems or something else I don’t understand. But to me, it seems like they are just cheap and don’t want to put another $50 part on a truck before selling it since most people might not use it.
So when you have trailer brakes on your trailer, which are required in most states for trailers of any weight, you have to hook them up yourself. Most vehicles come with a place on the under-dash fuse box that you can plug an after-market adapter into. Then you match the adapter wires up to an off-the-shelf trailer brake controller and you are good to go. But not the Hummer. I found this out the hard way when I orginally bought the adapter and controller months ago. For some reason, Hummer decided to use the normal adapter spot in the fuse box for the accessory lighting. The manual points you to this under-dash fuse box but its wrong. I verified this by asking a certified Hummer technician while visiting the dealer one day. He told me that GM reused the slot and now you have to hard-wire the brake controller. That means you have to run wires from inside of the H2 to inside of the engine yourself. Grrr.
I figured out how to get through the firewall a few weeks ago when I did my winch installation. So I mounted the electric brake controller up under the dash and ran the 3 wires from the controller up through the dash and out into the engine. The fourth wire stays inside the cab. You have to connect it to the back of the brake pedal switch. There was a whole group of wires coming off the brake pedal. I cut back the electrical tape, found the hot one with my meter, and connected to it.
Once in the engine, you connect 2 of the wires to the battery terminals. The other wire goes to the trailer hitch. This wire is a blue wire. You will find it laying near or inside of the fuse box inside the engine compartment. You may have to take the fuse box cover and casing off to find it. It will just be laying there. It has a black connector on the end. I cut off the connector and just used a standard jumper to connect my wire from inside to this one.
Then I hooked up my trailer and…it didn’t work. Hmmm. I went back through all the connections. Everything seemed OK. I was getting a 5V signal when the brake was off and about a 10V signal when it was on. I followed this all the way back to the hitch. Going from the truck to the trailer I have an adapter because the truck has a 7-pin connector and the trailer has a 6-pin connector. I tore my adapter apart and found out that it had the brakes in the wrong place. Supposedly, different manufactures put the brakes on different pins so you have to adjust. You just have to match the lines the whole way through if yours aren’t working.
After the adjustment, I tested again and it worked! I now have brakes on the trailer again. Hopefully, this post will help others who are interested in brakes to get the answers they need quicker than it took me. If you are and you want more pictures, let me know. I didn’t feel like getting under the hood again today.
