Wireinr my truck for trailer harness

[Has Been]

I have a 2002 GMC I bought used. I am trying to wire the harness for boat. Boat has 4 wire . Truck has no factory harness. It had A 5 wire to 4 conversion that was not working properlythat was on it. . Got a new one hooked it up , Get everything but break lights. Ground is good. Breaks into box, nothing out. Whats Up?

[LongLine]

HB - suggest yopu go to Harbor Freight on E Ridge & buy a 12v screwdriver type test light. (roughly $5) Best investment for trailer lights I ever made.

Also, with someone working the lights for you, check which filaments light up. Brightest ones should be the brakes.

I couldn't get my brake lights to come on couple weekends ago, but others worked. I found some corrosion inside the socket. Cleaned it & greased the bulb contacts ...Whoa-la , let there be light!

Tom B.

(LongLine)

[Trap Jaw]

On a 4 wire connector the turn signals and brakes are on the same circuit. Ie. left trun/brake and right turn/brake. What you're describing sounds like you have a broken wire somewhere. Since if you have turn signals you should have brakes, even if they are lighting the wrong filament in the bulb.

The problem with the way new vehicles are wired, you can't just splice into them for the trailer like older vehicles. You may be farther ahead to try and pick up a new harness for your truck. Definitely would save you some time.

[lakebound88]

check to make sure you got the right harness. did you get the one that just goes inbetween two plugs in the trucks main, or did the truck have one already spliced into it. go to the connection. probe it there with a test light or volt meter. keep in mind that it may be the wrong harness. hit reverse, if youre brakes light up then, then there ya go..ive seen it before on gm vehicles, a 2003 2500 in fact.

[Has Been]

I have all the right tools, tester,volt meter, crimps etc. I worked on it all day, checked & rechecked. Called Tech support 4 times. Checked ground , volts , etc. Even they were stumped. The last guy told me to wire it no more than 12 " from the truck tail lights. Said it needed to feel resistance for it to work properly. Did it & it works crazy as it sounds. They failed to mention that in the instructions. Thanks guys for taking time out of your day to offer help. Hope to do a shakedown within the next few days.

[Trap Jaw]

Wow, that's great. An electrical system that thinks.

What happened to the good old days when it worked or it didn't. Not like this, when the truck thinks it should.

[skipper19]

Electricity is too weird....like the bulb and the rest of the wiring was not enough resistance....hmmmm