Tow package - white wire

[HotWheelsBurban]

The best way to know 100% for sure, is to test the wires on the truck with a test light. If you don't have a test light, your local auto parts store has them for about $10. A test light will show the flashing of the blinker. If you use a test light, there is no mistake as to what is what.

Once you get the wiring harness sorted out, I would recommend having a test light handy if/when you rent a trailer. They're notorious for having bad grounds and sketchy lighting. I got a little thing that plugs into the 4 pin connector, that has LEDs in it and they'll light up when that circuit is activated. It's pocket sized and only around 6 or 7 bucks, so cheap insurance.

 

[Raspi454]

Once you get the wiring harness sorted out, I would recommend having a test light handy if/when you rent a trailer. They're notorious for having bad grounds and sketchy lighting. I got a little thing that plugs into the 4 pin connector, that has LEDs in it and they'll light up when that circuit is activated. It's pocket sized and only around 6 or 7 bucks, so cheap insurance.

Already got it all figured out, I need a new end tho, the one I had laying around was included with some magnetic trailer lights, and it's like 30 gauge crap wire, very brittle. Yes I have found my test light. That thing sounds pretty neat.

 

[HotWheelsBurban]

Already got it all figured out, I need a new end tho, the one I had laying around was included with some magnetic trailer lights, and it's like 30 gauge crap wire, very brittle. Yes I have found my test light. That thing sounds pretty neat.

It is. I got it at Northern Tool, but anyplace that has much towing stuff should have them. I found out that RockAuto has the Hopkins style plug in connector that goes into the rear light harness. Can't find the Hopkins anymore ( too many stores don't want to carry stuff for old trucks lol).

 

[HopHead357]

I stumbled across this while trying to wire up my camper shell 3rd brake light and interior light.

I found two bundles under the spare on my old body ‘99. One was basically directly behind the license plate (first picture). The other is above and on driver side frame rail. Comes directly off the connections that go into the brake lights (second and third pic). Also, there’s some sort of white tag that says “WHT FEED BRK SW-“ attached to a white wire (fourth pic). Is this the blue wire I need? Or this white one?

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[kennythewelder]

Double check, but the white wire is usually the ground wire.

 

[GMCTruck]

My 95 has a white wire running the length of the driver's side frame. It is probably 18 gauge. It is not a ground wire, it is for an auxiliary brake light.

 

[PlayingWithTBI]

Double check, but the white wire is usually the ground wire.

Yep, white usually is ground

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[GMCTruck]

Using my rudimentary microsoft PAINT skills;

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[HopHead357]

Using my rudimentary microsoft PAINT skills;

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OK, so the white wire was for a third brake light. I wired it up to my camper shell’s brake light and it worked perfectly.

The red and blue wire however I’m still unsure on. Anybody have any insight on those? I don’t really want to mess with then without knowing what they are. Did these trucks come with pre-wired auxiliary power?

 

[GMCTruck]

The red wire is for auxiliary battery charging and the blue wire is for trailer brakes. They are probably tucked up away beneath the brake booster and then they travel down the driver's side frame rail and then are just blunt cut at the end of the wire harness. in other words, pre-wired for aux battery and trailer brakes. If you don't use them, no problem.