outback_97 Posted May 13, 2010 Share Posted May 13, 2010 (edited) EDIT: Fixed it by running another ground wire from a tail light to the wiring harness. Hey guys, I'm trying to wire up a small utility trailer to tow with my '97. Here's what I have so far: A wiring converter spliced into the vehicles trailer wiring harness. A Harbor Freight utility trailer. I have the trailer wired up per the instructions, and when I connect the vehicle wiring to the trailer this is what I get. With key on and/or engine running and vehicle running lights off: All trailer lights function as they should. Brake lights work, turn signals work. With key on and/or engine running and vehicle running lights or headlights on: Trailer brake light and turn signal light works on the drivers side only. Passenger side does not function at all. In either of the above examples, the vehicle lights function fully, that is my brake lights and turn signals are functioning normally on the car itself whether or not the trailer is connected. What should I try? This is my first trailer wiring experience and I'm not sure how to troubleshoot this problem. Thanks! Edited May 15, 2010 by outback_97 Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted May 13, 2010 Share Posted May 13, 2010 First make sure you have the signal wires spliced into the correct wires in the harness. RH signal lamp power should be White/Red. LH signal lamp power is Light green/White. And double check ground connections for the tail lights as well as the ground connection for the trailer harness. Quote Link to comment Share on other sites More sharing options...
heartless Posted May 13, 2010 Share Posted May 13, 2010 (edited) first and foremost check all your grounds on BOTH sides and connections on the vehicle side - sounds like something may be hooked up wrong on the right side? verify that the turn signal/tail light wiring is correct for that side. i am gonna guess that the wires are backwards here & the right trailer turn signal - with running lights off - is dimmer than the left side? Edited May 13, 2010 by heartless Quote Link to comment Share on other sites More sharing options...
outback_97 Posted May 13, 2010 Author Share Posted May 13, 2010 Thanks guys. I'm pretty sure the wires are mated up correctly, I have double checked but I'll triple check. It was late last night when I was checking this out. It's just so odd to me (who doesn't understand how this works) that it would work fine with running lights off, then not work only on one side with running lights on. I did not notice anything dimmer on the right side but I'll check that out too. I think a ground problem is the most likely culprit. I could also switch sides with the tail lights on the trailer and see if the problem moves with them. Last night I had hit the troubleshooting wall so I just need to take a fresh look at it and try some new things, thanks for the suggestions! Quote Link to comment Share on other sites More sharing options...
Mike104 Posted May 13, 2010 Share Posted May 13, 2010 Trailer wiring drives me nuts at times. There were a number of threads on other sites about the trailer wiring converters being bad? I have had bad grounds between the trailer/car but it generally shows up as intermittent work/not work, that is not what you are saying is happening. HF makes a 4 pin trailer tester that has helped me in the past. I guess its either the converter, its wiring or the trailer. My bet is that its between the car and the trailer. Let us know how it turns out. Quote Link to comment Share on other sites More sharing options...
aa8jzdial Posted May 14, 2010 Share Posted May 14, 2010 Find a trailer with lights that work on a different vehicle. Hook the trailer up to your vehicle and verify the converter and your car wiring are ok. Hook your trailer to a known good vehicle. Is the trailer ok? I have been troubleshooting electrical problems for many years. Cut the problem in half over and over. Soon there is one thing left. (normally) Good luck Sometimes beer helps rick Quote Link to comment Share on other sites More sharing options...
outback_97 Posted May 14, 2010 Author Share Posted May 14, 2010 (edited) Great idea on the working trailer check, I had thought of that too but so far I haven't found one that has the same kind of connector (4 wire flat). I got the trailer wiring tester from HF for $4, and according to that, everything is wired up correctly on the car side. It's just LED's though, so I guess it wouldn't indicate if the power is a little low. I took the passenger side light off the trailer and both bulbs seem to work fine. I'll try to work on it some more this weekend and check all the connections and grounds. And maybe the converter is bad, I could try another one of those. Just found this in a thread about trailer wiring problems: http://www.skyroadster.com/forums/484514-post11.html The poster mentions running a dedicated ground wire from the problem tail light back to the white trailer ground wire. That's an easy one to try. And yes, a beer or several will help the process along! Edited May 14, 2010 by outback_97 Quote Link to comment Share on other sites More sharing options...
Cougar Posted May 14, 2010 Share Posted May 14, 2010 This is a stange one alright. I would have to suspect the converter is causing the trouble. The power for the taillights is causing the brake/blinker light problem. Also, if the grounding for the right side lights isn't wired like it should be I could see where power being applied to the running lights could cut off the return to ground for the brake/blinker lights. Quote Link to comment Share on other sites More sharing options...
outback_97 Posted May 14, 2010 Author Share Posted May 14, 2010 The lights are two-wire lights. So, they're self-grounding. The ground for the lights is through the mounting bolts, onto the mounting bracket, and onto the trailer. I didn't understand this at the time I had my problem, though it seems very obvious now. The paint on the trailer was preventing the ground. Therefore, the behavior of the light was that the tail-light wire was carrying the signal and the brake/turn wire was acting as a default ground. That's why things worked with the lights off -- there was only ever one signal being transmitted to the lights. But, with the lights on, both wires were carrying a signal and then the light had no ground and went blank. From this thread. I think I understand that, and if I'm reading it correctly, it explains why mine are doing this. Quote Link to comment Share on other sites More sharing options...
heartless Posted May 15, 2010 Share Posted May 15, 2010 one way to know for sure - unbolt the light, grind off a little paint, bolt the light back on and see if your problem disappears. Kind of thinking it just might. Good job finding that thread! Quote Link to comment Share on other sites More sharing options...
outback_97 Posted May 15, 2010 Author Share Posted May 15, 2010 Well, that was it I just ran an extra ground wire to the misbehaving tail light, and all is well. The trailer made her maiden voyage to Lowe's to get some siding today, worked great. We have named her "Clanky". Thanks for all the suggestions guys. Quote Link to comment Share on other sites More sharing options...
Suzam Posted May 16, 2010 Share Posted May 16, 2010 Good news that you got her fixed. I've had the same trailer with 8 inch wheels for 6 years. She comes in quite handy and has more than earned her keep and quietly sits folded in our garage until needed, and our MY01 Outback loves to pull her around. Quote Link to comment Share on other sites More sharing options...
Kgaleher Posted July 21, 2016 Share Posted July 21, 2016 Electrical people: Im a single mom. My 14 year old and I wired his trailer. All the lights work (side, break, turning, hazards) as long as the headlights are off. Once you turn the headlights on - back lights don't work at all, side lights still work. I've grounded everything, cleaned all connections, etc. Nothing helps. Any ideas? Thanks! Quote Link to comment Share on other sites More sharing options...
mdconvert Posted July 21, 2016 Share Posted July 21, 2016 Sounds to me like there is a short between the ground the the tail light bulb. Quote Link to comment Share on other sites More sharing options...
Kgaleher Posted July 21, 2016 Share Posted July 21, 2016 Thanks! Any tips on how I can fix it? (from a clueless mom Quote Link to comment Share on other sites More sharing options...
mdconvert Posted July 21, 2016 Share Posted July 21, 2016 This is interesting. I may take back what I said about this being a short between the tail light and ground since the side lights stay on. If the tail light isn't working I would expect that the side lights would not work too. Sorry, I'm as puzzled as you are. Quote Link to comment Share on other sites More sharing options...
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