Can someone figure this one?

[Hemlock]

Yet another trailer light issue...<br />Symptoms/Facts:<br />1996 GMC Jimmy<br />Small boat trailer newly wired<br />All lights work when vehicle lights are on<br />Center LED brake light is out on Jimmy<br />When I press brake, all trailer lights go off<br />When I had cruise control on, and put turn signal on, it would cut out the cruise.<br />Jimmy also used to blow 20A fuse (brake light/chime) as I touched the brakes and have beefed it up to a 30A.<br /><br />Where is the problem(s)<br />Trailer is fine with another vehicle. WHere in my Jimmy should I start looking?

 

[braindead0]

Re: Can someone figure this one?

When I press brake, all trailer lights go off

'go off' as in go out, or turn on? Including the taillight element? I presume you're on a 4-wire trailer connection (ground, tail, left brake and right brake)? Are the taillights on the Jimmy seperate brake/tail elements or bulbs?<br /><br />How did you wire into the harness? <br /><br />Here's a crazy thought, they may have used the LED brake light as part of the circuit, if it's either shorted out or open perhaps it could be messing with the circuit.<br /><br />I would expect the cruise to cut out when the brake is pressed... which it may get from the brake light circuit. As the brake lights and turn signals use the same bulb element (I suspect) then if the center brake light LED is shorted it could allow current to make it to the brake circuit.<br /><br />Without the trailer connected, if you turn on your left or right turn signal, does the other side light up as well?

 

[Hemlock]

Re: Can someone figure this one?

Braindead0,<br /><br />I have a lot of confidence in you, going by your name....j/k.<br /><br />I'll try and answer some of your questions. When I put my brake on, the trailer lights go off, ka-put, out, dark, nothing. Yes I have a four wire harness. One of your last questions about turn signals? Truck does not do anything funky when it's not hooked up to trailer...other than the center brake light not working.

 

[bhalsdorf]

Re: Can someone figure this one?

Almost sounds like you have one of the wires hooked up wrong in your Jimmy. If it's working properly on another vehicle. When you had it hooked to another vehicle everything worked fine? Brake lights and signal lights? If so then recheck the wiring harness for the trailer that's in your Jimmy. You may have a wire or two that got hooked up wrong.

 

[braindead0]

Re: Can someone figure this one?

Did you wire up the trailer plug (on your truck) yourself? Or use a manufactured harness connection?<br /><br />Does sound like the wiring isn't quite right. If you (or even a shop) attempted to splice into the wiring harness, I'd suggest getting a manufactured plug setup that plugs into the wiring harness.. they are cheap and I've never seen one of those done incorrectly ;-)

 

[poolshark38759]

Re: Can someone figure this one?

one other thing to check would be the turn signals on the jimmy....do you have the amber turn signals on the rear?? this could cause the problem and you might need a converter...being i a 96 i dont think so but you might have over looked it..just a thought and my two cents worth...

 

[dakotashooter2]

Re: Can someone figure this one?

Did you splice in the harness yourself or is it a plug in or T harness? If a plug in is it a factory harness or aftermarket brand? Every aftermarket harness I have tried has caused problems because of a srewed up ground in the harness.

 

[braindead0]

Re: Can someone figure this one?

Every aftermarket harness I have tried has caused problems because of a srewed up ground in the harness.

That's odd, both my 1994 S-10 and 1999 S-10 have aftermarket trailer wiring harnesses and they worked fine. I'd imagine his Jimmy is nearly identical.<br /><br />I've installed aftermarket harnesses on at least 6 other vehicles, with no problems. perhaps it's a certain brand?<br /><br />In fact, every one I've ever installed requires you to attach the ground wire to the frame/body and doesn't pull ground from the harness.

 

[kdmiller8251]

Re: Can someone figure this one?

One other thing...<br /><br />By the fact that you had to "BEEF UP" one of your fuses...... You got a short somewhere that needs to be fixed..... You shouldnt have to change your fuse to a bigger one...<br /><br />The center light being out could be a major problem... My dad had one that went out and the cruise wouldnt work and there were some other problems... That could be part of it...

 

[Hemlock]

Re: Can someone figure this one?

Thanks for all your replies. I will print this thread off and explore all possibilities. <br /><br />As far as I know, the wiring was done by a GM dealer, but I will check. What is the best way to explore that one? How far (in feet) do I have to follow the trailer wires to the front of the truck to determine that? The center brake light has been out for months, but never affected anything, including cruise. The only time I've had problems is while hooked up to trailer.

 

[braindead0]

Re: Can someone figure this one?

If the dealer's trailer wiring is run the length of the vehicle, I'd suggest removing it (cutting and sealing with liquid electrical tape..and regular electrical tape should do it) and replace that with a plug in trailer wiring harnes from a auto parts store. <br /><br />These just plug into the existing wiring harness, usually there is a factory plug on the drivers side right near the rear bumper, these just plug in between. Worked like a charm on both my S-10's which should have nearly the same wiring as your Jimmy.

 

[Kenneth Brown]

Re: Can someone figure this one?

Another one of those your not gonna believe its. Pull your lenses and look where the wires go into it. See if you see anything abnormal, especially melted plastic. My wifes van, 99 Montana, developed a problem similar to yours, only it did it all the time. I found the ground wire had come loose from the harness and it was "back tracking" through the system to find the ground. It would do all sorts of neat things. I simply soldered a new wire into the light assembly witha bullet connector on it. I then put the other side of the connector on the harness and hooked it all up, its worked fine now for about a year.

 

[DJ]

Re: Can someone figure this one?

Hemlock,<br /><br />Keep thinking: ground, ground, ground.<br /><br />Get a cheap 12 volt test light. Hook the clip end to a known good ground on the truck. Probe each of the truck plug connections to see if that particular thing works-turn sig., brake, run lights. If they work OK with the test light, you have a truck to trailer ground problem. Or, a short in the trailer. I'm beting ground issue.<br /><br />Also, lose that bigger fuse. It SHOULD NOT blow fuses. The bigger fuse may cause bigger problems like melted wires where you can't see them.

 

[Hemlock]

Re: Can someone figure this one?

Alright, will keep figuring things out by process of elimination. Trailer lights are such a pain...

 

[lakeman1999]

Re: Can someone figure this one?

Trailer lights are no problem, all you have to do is trace the circuits down. Start, by using a test light like djohns19 says, on your pigtail from the vehicle, if every thing works ok there, then start checking every thing on the trailer. Just make sure you have a good ground hard wired from the vehicle, to the trailer. And that means to drill a new hole in the frame (a heavy piece of metal in the fram), and bolt the vehicle pigtail ground here, preferably with a tapped hole, and screw, or with a self tapping screw. Then drill a new hole in the trailer, in a beefy part of the trailer, and do the same with the ground from the trailer pigtail. You may have to go back to every light, and remove, and file off paint where it attaches to the trailer. Many times a ground is not enough, you need a very good ground on every light. And never depend on the ball and socket to make your ground.

 

[bgoad]

Re: Can someone figure this one?

Hemlock,<br /> Just so you know that you're not the only one with that problem.<br /> I also have a 1996 Jimmy and my trailer lights do the same thing. When I have my headlights on and hit the brkes my trailer lights go out. <br /> I have not used the cruise control.

 

[braindead0]

Re: Can someone figure this one?

That sure is odd, I wonder if there are some bad harness plugs out there.. I've never seen any myself, but this sure is strange.