1991 K5 Brake Controller Question??

[frankc]

I'm having (or doing it myself) a brake controller installed and I believe the wires are already bundled under the rear bumper and in the engine compartment/driver side (red and blue wires). The end of the blue wire is accessible, but the red wire runs to a terminal box on the firewall on the drivers side of the air cleaner.

When I talked to someone they said the red wire needs to go to the + of the batt.

Question: Why is it connected to the electrical box? What is that terminal box used for?

From that terminal box another red wire runs down along the firewall, and another to the left (passenger).

Any info would be great! I have to tow a trailor to a campground this weekend and I waited to the last minute to do this!

 

[jeff in co]

I use the pictured box as my "true battery" connection when a device is asking for constant battery power. I think it would be adequate for your trailer to be connected here as well (instead of directly to battery).

And if I recall, the red/blue bundle goes to the back end so dig around there.

 

[dyeager535]

That is typically referred to as a junction block. Get your voltmeter out and verify, but that should be 12V battery, or the truck won't run.

Pretty sure there is a light blue wire and orange with black(?) stripe that runs the power tailgate window motor (assuming you have one), you sure there is a spare blue wire there? I'd have to look at my trucks, but I do recall there being some bundled up heavy gauge wiring near the junction block, maybe red and dark blue?

You'd want to wire your brake controller up however they tell you to. That junction block isn't fused (fusible links protect the system) however if you need battery 12V to the trailer brakes, this is where I'd do it.

If you need power feeds for the controller itself, you can use spade terminals (temporarily IMO) and connect those to the rows of empty slots at the top of the fuse panel. They should be marked when they are hot. (batt, ign, etc) SHOULD be marked...again test with voltmeter. Make sure to fuse them properly, those accessory rows are all on 30A breakers as I recall. Do NOT tap or splice into anything, there should be nothing that needs you to do so, and that will cause very bad headaches later.

Improper trailer wiring is IMO probably the number one source of electrical problems on these trucks, do it right so you don't end up with the difficult problems bad wiring presents.

I assume this is being done with a 7 pin connector? Make sure that is wired up correctly too...nothing more frustrating than trying to hook up a trailer and finding the vehicle is wired up wrong, or vise versa.

 

[frankc]

Thanks for quick replies, advice on splicing, and true 12 v connection. Yes the junction block does have 12v.

Under the rear bumper, there was the red and blue wires (which are connected) as well as 2 greens, yellow, black and white, (white was larger). I assume I was wired for a brake controller from factory. This does not include the power window wires, which I do have and yes it is orange/black.

I believe the blue wire is for the controller to 7 pin connector.

BTW, regarding the junction block, it looks like the fan blower/AC is connected (red wire going left) as well as 2-3 other red wires heading downward rear into wire loom(rear engine). Which is a 6.2 diesel (btw),

 

[dyeager535]

Heater one is probably for the "high" setting on the fan, as that doesn't use a resistor, it's 12V directly to the motor.

Assuming you can find the termination of those wires, I suppose you are good to go...there are two connectors for the rear window, one connector feeds the motor directly (from the dash switch, through the safety switch in the tailgate, to the motor) the other connector wiring goes to the key switch. Tailgate wiring colors on my '85 are: lt blue, brn/wht, orn/blk, and blk.

I assume you'd figure that out because they are connected, just not sure what you are looking at for wiring back there.

Just went out and checked my '87. There are very thick red and blue wires both hung up near the junction block, and zip tied in a bundle (with a factory plastic clip taped to them) at the rear of the truck. The red wire has what appears to be an inline fuse holder near the junction block which does not appear to be an aftermarket unit.

There is one of the 4 flat trailer adapters that goes between the lights and body harness, but that may or may not be factory. I'd have to check the RPO tag, I suspect trailer wiring of any type should be an RPO if factory. Since the red and blue wires aren't connected to anything, I can't imagine any reason that would be aftermarket...pretty sure another truck I dismantled had the same/very similar wiring on it.

 

[jeff in co]

Heater one is probably for the "high" setting on the fan, as that doesn't use a resistor, it's 12V directly to the motor.

Assuming you can find the termination of those wires, I suppose you are good to go...there are two connectors for the rear window, one connector feeds the motor directly (from the dash switch, through the safety switch in the tailgate, to the motor) the other connector wiring goes to the key switch. Tailgate wiring colors on my '85 are: lt blue, brn/wht, orn/blk, and blk.

I assume you'd figure that out because they are connected, just not sure what you are looking at for wiring back there.

Just went out and checked my '87. There are very thick red and blue wires both hung up near the junction block, and zip tied in a bundle (with a factory plastic clip taped to them) at the rear of the truck. The red wire has what appears to be an inline fuse holder near the junction block which does not appear to be an aftermarket unit.

There is one of the 4 flat trailer adapters that goes between the lights and body harness, but that may or may not be factory. I'd have to check the RPO tag, I suspect trailer wiring of any type should be an RPO if factory. Since the red and blue wires aren't connected to anything, I can't imagine any reason that would be aftermarket...pretty sure another truck I dismantled had the same/very similar wiring on it.

I have the same red and blue thick wires running to the back. This was basically a pre-wire for trailer brakes from the factory. Although I don't have a trailer brake controller inside the truck, I just hooked up a 7 pin outlet in the rear (replaced an older 6 pin plug). I only utilized the standard 4 wires plus the backup signal. I did not connect the 12V constant or the Brake controller input. I just don't plan on using those for my boat trailer.

I needed the backup signal to release the disc brakes on my trailer....other wise they would sit in the locked position when backing up (which makes it a lot more difficult!)

Anyways, I did re-wire my boat to have the standard 7 plug design but what I found was the color of wires within that plug did not necessarily corrolate to the colors on the truck receiver plug. Kinda strange really.

I used my Yukon XL factory 7 plug as the standard and made sure the boat and Blazer had the same configuration. And it must be right because my brother just pulled my boat back from Idaho with his 07' Tahoe and everything worked as it should.