Trailer Brake Controller Problem

[Gary the Engineer]

Originally posted this in the C/K forum by mistake.

I recently purchased an auto hauler and had a HOPPY brake controller installed by the trailer dealer. He hooked up the controller to the under-dash junction box. He just plugged in the after-market adapter into it.

Now here's the problem. I get a variable voltage from the controller if I adjust the thumb wheel on the controller. However, I get a constant 11.5 volts at the 7-pin trailer connecter when I step on the brakes. Darn near put me through the windshield. I was hauling a car from SC to MN at the time. It was more dangerous to run with the brakes on the trailer hooked up, so I disconnected the blue wire from the harness and just gave myself some extra stopping distance.

Is there a relay or something between the plug-in at the fuse box and the wiring at the rear of the truck? I assume my truck has the tow package standard as I have the tow button on the handle on the steering column. Of course I have pushed the button and do not get an indication light on the dash as I should.

Until I can figure out this problem, I am going to bypass the internal junction box and run an external (outside the firewall) blue wire from the controller directly to the 7-pin connector for the trailer.

Anyone else had this issue or know how to solve it?

Thanks.

[maxwedge]

Where do you get a variable voltage from the controller, that disappears by the time it reaches the trailer connector? No relay the wire coming out of the control for the power to the brakes should vary by the amount the pedal is depressed and the thumb wheel setting. The tow mode button delays trans upshifts for better towing power as I assume you know.

[Gary the Engineer]

I probably didn't make myself clear...when I check the voltage coming from the controller at its minimum setting, I get 1.5V. As I turn the adjustment wheel on the controller the voltage increases. I did this to ensure that the controller was not the problem. Still trying to see why I get a full 11.5V coming from the connector at the back of the truck as soon as the brakes are applied.

I did find the literature from Hoppy and it stated that for Chevy trucks that do not have the tow package installed, the brake wire and the power wire require them to be run outside the firewall. That is, a separate wire going from the controller to the connector at the hitch.

We will see...

[EA6BMECH]

Well I know they can be hooked up wrong. 1st time for me the trailer people hooked mine up. Hit the brakes and nothing. Hit the rheostat and wham!!!! all the brakes at one time. Somehow they hooked the brake switch wire up wrong. Been many years, but I fixed it.

[3alix]

If the blue wire that you talking about is the one from the factory prewired trailer wiring harness, it is for the third brake light.This would be used to wire a third light on a canopy and always sees about 12 volts dc.when the brake is applied. The factory owner's manual that comes with the truck has a section in it that will ID the proper wire that you should use.Hope this helps.

[jeep_cj4x4]

3alix is right about the 3rd brakelight wire. I made that same mistake when I hooked mine up. I ended up going down to the local trailer shop and had them hook mine up the rest of the way. I figured all I had to do was plug in to the block under the dash like you did but there are a couple extra conections under the hood that the manual doesnt mention. Also need to run an extra wire to the rear of the vehicle and splice in to where the plug is... here are two pictures of the splice under the hood inside the fuse box and an extra fuse that needs to be installed (30A), and the last pic is of the splice at the rear from the wires they ran along the frame. let me know if you need more explination.



The red wire needs to be hooked to the stud and spliced into and the blue wire needs to be spliced into also. Those two wires need to be ran to the rear of the truck to the connector.



I'm not sure which large 30A fuse it was (just compare which one is missing from yours) but it needs to be added so you get power to the stud with the red wire you attached.