Finding a short

[Stormy Weather]

I have a short somewhere between the Bargeman connector and my tail lights on my '73 Tradewind...the trailer taillight fuse blows on my TW whenever I turn on the headlights. Questions: where to start to locate the short? What side of the trailer does the wiring go down (under the underbelly - ugh!)? Is it the green wire that I'm tracing or the red? Any information and suggestions would be greatly appreciated.

[TG Twinkie]

I should be the green wire, the red will be the left turn signal. I would start by removing the bulbs in all of the exterior lights; tail and marker. If the fuse holds, replace the bulbs one at a time. If not look for chaffed wires at the fixtures.
I believe the wiring runs between the inner and outer skin above the floor, not in the belly pan area.

[submariner]

just put an oversized fuse in and where ever you see smoke.. there is your short easy

[HowieE]

I would disconnect the umbilical cord just inside the trailer and check which side of that open the short is before I would go into the trailer itself. Older cords sometime have a problem within the cord.

[wasagachris]

If the fuse blows when the headlights are put on then the short is in the running light circuit and could be at any of the clearance lights or at the taillights itself. The harness runs along the ceiling just inside of the center strip of interior skin along the curb side. You will have to check all the clearance lights as well, most likely it is shorted or broken at one of the connections to the lights and not in the main harness itself.

[Stormy Weather]

Thanks for everyone's comments. Great advice...except from Submariner...something about using smoke to detect a problem doesn't sound overly safe...I appreciated the humor however after a frustrating weekend! I did pull the rear marker lights yesterday looking for a leak culprit. I might have done something during that process. I'll pull them all off again and pull the lights out and see if the fuse blows and then start replacing one at a time.
Incidentally, what is the best way to prevent water leaks where those rear marker lights are attached?

[Jammer]

Originally Posted by submariner

just put an oversized fuse in and where ever you see smoke.. there is your short easy

Originally Posted by Stormy Weather

Thanks for everyone's comments. Great advice...except from Submariner...something about using smoke to detect a problem doesn't sound overly safe

It's actually a legitimate troubleshooting technique but I would never use it in a situation like this where the wires are hidden and could pose a fire hazard.

I did pull the rear marker lights yesterday looking for a leak culprit. I might have done something during that process. I'll pull them all off again and pull the lights out and see if the fuse blows and then start replacing one at a time.

I usually look for shorts by inspecting the wiring visually. Usually there is more than one bare spot in the insulation when this happens. You can check behind the taillights, yes, try to look at as much of the wire as possible. Then check around the umbilical. Usually the failures occur someplace where the wire goes through the frame.

You may also find that there is no short at all but rather just insufficient tail light wiring in the tow vehicle. I wire a relay and a separate towing circuit for the running lights to increase capacity and help with fault isolation. Some newer tow vehicles are already wired that way.

Incidentally, what is the best way to prevent water leaks where those rear marker lights are attached?

Vulkem or parabond, check the "caulks and sealants" subforum.

[Stormy Weather]

Pulled out all the marker lights and the tail lights. Even took the marker light housings off the trailer in case it was a wiring problem. Turned the lights on at the TV. One by one put all the lights back in their sockets. They all worked. So now I knew that it must be a wiring problem. One by one attached the marker lights back onto the trailer with bead of vulkem seal. At this point I learned that the screws that hold the marker lights on the trailer are actually the ground for the lights. Interesting. I started a the front. The PO used 2" self-tapping metal screws half of which were stripped (a project for next weekend). Got to the back of the trailer and found that when I screwed one of the screws all the way in on the center marker light, the fuse blew. So at this point I knew it either had to be the smashed marker light wire that was shorting out, or the screw was being screwed into the wire, or something, between the outer and inner wall. Replaced the fuse (about the 5th one by now!). Twisted, pinched, etc. the light housing and wire in all possible ways. The lights still stayed on. So I suspected the screw had to be the culprit. I used a rivet to attach the light (which is probably what should be used) and the lights stayed on! Mystery solved.
Lessons learned:
- Never use 2" screws to attach anything to the exterior or interior walls.
- Need to replace the marker lights with a better quality. Need to figure out how to install so that the lights fit tight against the skin. The wiring didn't fit very well behind the housing. Thinking of possible LEDs.
- Be persistent and methodical, eliminating probable causes along the way
- Use this forum! The people here are knowledgable, friendly, and anxious to help. Thanks guys!

[Andrew Selking]

A little more humor My electrical friends tell my you only get to let the smoke out of the wire one time. After that it is all over time for new wire. Glad you found the problem.

[TG Twinkie]

It's TRUE: "All electrical devices work on smoke" Because when you let the smoke out, it doesn't work anymore. LOL