Posted 2011-01-19 4:39 PM (#129046) Subject: Tail Light short
Expert
Posts: 2453 Location: Northern Utah
Got a short in my trailer lights that is driving me crazy.
Brake lights and turn signals are working fine, But I have no running lights.
Which include no tail lights or any of the marker lights.
I started off making sure that the plugs on both the truck and trailer were working. And I did have a blown fuse on the Ford truck. So what ever has shorted, blew the 30 amp maxi fuse. ( on a side note, changing that fuse on the 2011 Ford was a PIA, Ford really blew it with the location of the fuse panels)
After replacing the fuse, I can insert a test plug and get all the LED to light up, So I know the truck is functioning correctly. So now to tackle the trailer.
The only fuse I'm aware of on the trailer is next to the twin batteries and I assume has nothing to do with tail lghts. It only serves the batteries. But regardless, I replaced it and made sure it was good. Still no running lights.
I'm just afraid that the fault will be deep inside a channel of the trailer and had to find.
Posted 2011-01-19 7:58 PM (#129049 - in reply to #129046) Subject: RE: Tail Light short
Expert
Posts: 3853 Location: Vermont
First - check the ground. Next: The running lights can be a constant source of trouble, especially on aging trailers. The electrical connections are subjected to varying degrees of temperature changes, humidity levels and road vibrations. This leads to a build up of corrosion on the contact areas and frequent light outages, which always seem to crop up at night (naturally).A short circuit can be caused by wires that are constantly rubbing against the frame or other metal object. A screw or staple, inside the walls or ceiling, may have punctured the wire. Have you added any accessory on the coach that may have put a mounting screw though the wiring? Once the insulation on the wire has worn away, the circuit shorts to ground and the resulting high current flow blows the fuse. Finding the problem involves a step by step investigation.The clearance lights are normally wired in parallel - there should be a "hot" wire and a ground for each light. (Some outfits used the metal skin as the ground path - others have a separate wire for this purpose.) The power wire connects to the light and also carries on to the next light in the circuit. Usually it is the green wire that is the hot wire. Disconnect the power source ... Remove the trailer plug from the tow vehicle and disconnect the trailer battery ... Remove the cover lenses and the light bulbs from every clearance light and both tail lights. Start with one of the front side clearance lights, assuming that they will be first in line. Remove the mounting screws and pull the light away from the wall to access the wiring behind it. Disconnect and separate the hot wires that lead to that light. With an ohm meter, test the wire that leads from the power source (trailer plug) to that light. The negative probe of the meter is touched to a ground source and the positive probe to the bared wire end.If the meter shows continuity on that wire, that's the faulty run. If that wire shows no continuity, test the wire that goes to the next light. If that wire shows continuity, leave the light disconnected and continue to the next light and repeat. If the wire that runs between the lights is shorted, the meter will show continuity. Keep going until you isolate the shorted run. Hopefully it's in the first few lights.
Posted 2011-01-20 11:19 AM (#129067 - in reply to #129046) Subject: RE: Tail Light short
Expert
Posts: 5870 Location: western PA
We had a momentary running light short that would blow the truck's fuse. To no avail, we literally spent months trying to find the source, and installed countless fuses. Went to NAPA and bought an autoreset circuit breaker that fits into the fuse spot. It's been there several years and we always have running lights when we need them. No more blown fuses.
Posted 2011-01-21 2:15 AM (#129098 - in reply to #129046) Subject: RE: Tail Light short
Expert
Posts: 2453 Location: Northern Utah
this trailer uses the trailer metal as the ground. If the ground was bad, All of the lights would fail to function. My brake, turn signals, floods, and interior lights still all work, So I don't think it is the main ground. And I don't think I could have the invidual grounds on all marker light ( about 12) and the tail lights fail at the same instant. So first thoughts are that it's not the ground. I did open the plug and insure that all connections were good at the plug and that my main ground by the batteries was tight and had a good connections.
Since the marker lights run in parrallel, I suspect the problem will be somewhere that there is a junction that has come loose or a wire has rubbed the insulation off. It' will be a time consuming project to trace the wiring through all the channels and conduit of this trailer.
Posted 2011-01-23 9:54 AM (#129162 - in reply to #129046) Subject: RE: Tail Light short
Expert
Posts: 2453 Location: Northern Utah
Found the problem.
This trailer has junction boxes between the axles on both sides. Out of this junction box comes a wire for the fender marker light. When I had the blow out last Oct the flapping rubber must have tugged on that marker light wire and it came loose or has worked loose since then. It had grounded itself and shorted out all the running lights.
Wire nuted everything back tight together and wrapped it in electrical tape,, Problem fixed.
Posted 2011-01-23 10:17 AM (#129164 - in reply to #129162) Subject: RE: Tail Light short
Expert
Posts: 3802 Location: Rocky Mount N.C.
Originally written by Painted Horse on 2011-01-23 10:54 AM
Found the problem.
This trailer has junction boxes between the axles on both sides. Out of this junction box comes a wire for the fender marker light. When I had the blow out last Oct the flapping rubber must have tugged on that marker light wire and it came loose or has worked loose since then. It had grounded itself and shorted out all the running lights.
Wire nuted everything back tight together and wrapped it in electrical tape,, Problem fixed.
That was from when you lost your spare and it caught and bent the trailer axles...??
Posted 2011-01-23 4:52 PM (#129177 - in reply to #129046) Subject: RE: Tail Light short
Expert
Posts: 2453 Location: Northern Utah
Yes. I'm still fixing things because of that incident last October.
I didn't notice that my running lights were not working until just recently. I suspect that the wiring got stressed and fnally pulled apart and shorted out. But I haven't towed a lot because of winter and what towing I have done, has been in the daylight.
Tail Light short
