View Full Version : Trailer light problems

06-28-2003, 08:50 PM
I got new truck and was hooking up the wiring harness when I discovered a strange problem. When my truck lights are off, everything works fine, brakes, blinkers etc. When my truck lights are on, the lights work and blinkers work but when you put the brakes on, everything goes off. Any ideas?

Brian Raymond
06-29-2003, 12:06 AM
If it is an older model(4plug), There may be a internal issue on the trailer plug-in, can be rendered by splicing in a new one, not saying for sure that is the prob., but sometimes have run across.Brian Raymond

06-29-2003, 07:31 AM
It is the 5 flat on a 2001 Outback. It has to be something in the trailer because I had my neighbor come over and hook his truck up and it did the same thing. The strange thing is that I did not notice this problem until hooking the new connector up. I THINK that it was working right with my suburban. I may try splicing in a new connector on the trailer. Thanks Brian. If anyone else has any thoughts, please let me know.

06-29-2003, 07:53 AM
You might check or replace the tail light bulbs. I've seen a bulb on a car where one of the filaments broke and crossed another filament within the bulb, causing overall weirdness ( can't remember exactly what it did, but brakes and lights were involved).

Other idea: sounds like might want to take a pad and paper and continuity meter and run down each wire, starting with the tail lights.

Last thought... that fifth wire has always bugged me.... mine dead-ends in the trailer tongue. If it were hooked-up to a tow vehicle it would short-out. ( It isn't because I have a 4 wire connector on the tow vehicle.) The forum said this connects the back-up circuit on the vehicle to the brake-release solenoid on the trailer...mine doesn't have the solenoid... I presume yours does. But if yours ddoesn't, I'd ensure that the dead-ended wire is capped-off w/ wire nut and tape....

07-07-2003, 05:36 PM
Your getting a feedback loop through your tail lights. Check your bulbs as mentioned before and verify you have a good ground at the connector and also at the tail lights as the travel of least resistance appears to be through your tail lights when they are on. You might notice your brake lights are a little dim due to the resistance to ground. Good luck.