View Full Version : Truck/trailer lighting problems???

03-09-2009, 12:40 AM
I have all chevys/GMC 3/4 trucks. There 2003 thru 2009. My 07.08,09 all blow the fuses when I plug the trailers into them. The 03,04 have no problems at all. We hook up and every light is running. When we hook up to the newer trucks, the fuse blows and all we have is brake and signal lights - no running lights - which ya need at night. Any ideas?

All trailers are new within the last two years. LED lighting, ect.

03-09-2009, 01:15 AM
Sounds like a short somewhere on the trucks. Check the ground on the plug of the truck and also on the trailer. Hope this helps a bit, good luck.

03-09-2009, 05:00 PM
Maybe the fuses are too small for the electrical load. What amp fuses are in the older trucks, compared to the new ones? Just a thought.

03-09-2009, 05:18 PM
Fuses are 10 amp a piece for left and right turn signals. I think the marker lights are either 10 or 15 amp. I just wonder why you are having problems on one set of trucks vs the others?

I would even try to check Chevy forums to see if they have issues.

03-09-2009, 08:27 PM
Running all 15 amp. All trucks are the same. I went to 20 amp thinking more is better but it didn't matter - they still blow.

03-10-2009, 12:30 AM
one question can you hook up the trailer to another truck and not blow the fuses ?some thing is pulling way to many amps the led lights should not pull to many .change to another truck completely and see what it does . i would hate to think that the 07 08 09 have that fragile a running light circuit do they have factory plug's on them or have they been added on ?

03-10-2009, 12:54 AM
Are you running the 4 flat or the round plugs?

ALLPro Landscaping
03-10-2009, 01:01 AM
I would check the wiring on the trailers, before anything, How old are the trailers, was anything done to the light on the trailers in the past, Check that before anything else, what type plug are you using, if the trailers are wired correctly call up your local dealer and get a trailer lighting wire diagram, make sure thats right, I would usually say you have a bad ground, but if its only happening on your new trucks, their is something not right on the wiring. Also check and make sure the ground is correct inthe plugs truck side and trailer side, I know some trailers have different wiring.

03-10-2009, 01:18 AM
Trailers are 2 years old, there is a wiring diagram in the back of the operators book in the glove box.

Might need to take on off the lights off, get some test wires, and go behind the truck and hook one light up and try it that way, may be a pain, but something has to give.

03-10-2009, 01:26 AM
Trailers (2) were new last summer and bought exact same trailer last fall. From day one I have fought this issue. Called the trailer people and they say bad fuse ot truck problems. Since then I have added an 08 and 09 GMC 3/4 trucks with no avail. Yet when I plug each trailer into the older trucks - everything works.

Trailers came with round plugin. I have not added or taken away from trailer light or added anything to trucks. The 07,08,09 trucks all have plows and sanders on them. Could this be an issue.

What is odd though is I have two flat bed trailers that when hooked up to the new trucks, everything works, but hook up to the older trucks, then just brakes and singals work - exact opposite.

I am tire of trying, having people look and no one seems to know anything so now I have turned to the professionals!! That you guys!!

03-10-2009, 01:31 AM
So..... you have a good set of trucks and trailers paired up that you have no problems with, and when you do a switch, that when the problems arise. Well, There is probably a different wiring schematics for the 2007 + GM trucks, excluding 2007 classic. If You have the book for each truck, 2005 vs 2008, read each of the wiring diagrams in the back and compare the 2. There has to be a difference if they are doing these problems. It has to be something in the truck wiring on the new one that is different from the older models.

ALLPro Landscaping
03-10-2009, 01:36 AM
Their is definitely a different wiring lay out on the newer trucks compared to the old.

03-10-2009, 01:36 AM
I know for a fact that Oklahoma trucks are wired different than all the other states.

ALLPro Landscaping
03-10-2009, 01:38 AM
Why is that

03-10-2009, 09:39 AM
I have no clue, but that is just the way those trucks from there are, I never understood why.