1

A couple of questions: I have a camper trailer that apparently has a dead short in either the positive or ground wires between the battery and the fuse panel. Someone told me to measure the resistance of the hot wire and ground wire from the fuse panel back to the battery. He said if the wires are good the resistance will measure zero ohms. I measured the resistance in both wires and they measured zero ohms. If the wire did have a short, what happens to the ohms reading when I measure the resistance? Is there no reading on the ohm meter or does the number of ohms measured rise dramatically?

The fuse panel: When I removed all of the fuses and add them back in one fuse at a time I found one fuse in the panel that when I replace it, it causes the main fuse to blow. Yet when I measure ohms across the fuse panel from the positive terminal to the negative terminal I get a reading of zero ohms. If the fuse panel is bad why would I get a reading of zero ohms?

longtimealaskan
  • 11
  • 1
  • 2
  • 1
    you need a better meter reads milliohms and tracing skills . one method is to put a heater or lamp between power and fuse panel and measure voltage thruout. Another method puts an RF signal current across fuse panel with main open and trace the signal with a special radio – Tony Stewart EE75 Oct 16 '16 at 01:07

1 Answers1

1

You have narrowed down the short to one circuit. I'll assume the camper trailer is conventional automotive negative ground with +12 fused.

So there is a short between the circuit you have identified and ground.

schematic

simulate this circuit – Schematic created using CircuitLab

When the fuse you have identified (F5 in my schematic) is removed you should have no voltage relative to ground on one side of the fuse holder (and 12V on the other).

At this point you have identified the wire that is shorted and there is not much else you can do with normal test equipment. The exact resistance and the wire gauge will give you sort of a hint as to the location, but not much more than a hint.

What you have to do is to trace the wire from that fuse holder to wherever it goes and fix the short (maybe it is pinched where it goes through a door hinge or the insulation has cracked where there is pressure on it). You should be able to figure out what it powers since that is the thing (or things) that will not operate with the fuse removed- everything else should work. Maybe there are markings that are a hint on the fuse box. If it is just one thing you could consider cutting the wire at the far end and bypassing it with a new wire. Of course if you have a proper manual for the wiring it should show you the wire path, color codes, splice locations, ground connections and so on for the entire harness.

If you can provide some photos and detailed information the mechanic SE could be of help- I'm sure this problem comes up in maintenance of classic cars.

Spehro Pefhany
  • 376,485
  • 21
  • 320
  • 842
  • Thank you for your detailed response. First I need to correct something I said earlier. There were two fuses on the fuse panel that caused the main fuse to blow. One of the fuses is labeled "Reverse Protection" and the other is labeled "Battery fuses". – longtimealaskan Oct 16 '16 at 08:12
  • I disconnected wires for interior lights, stereo, furnace, refrigerator, and water pump from the fuse panel, leaving only hot wire and ground wire attached. The main fuse blew. I removed all fuses from the fuse panel and replaced them one at a time. I replaced the interior lights, stereo, furnace, refrigerator, and water pump fuses without blowing a fuse. Replacing the fuses labeled "Battery fuses" or "Reverse Protection" blew the main fuse. I traced the hot wire & ground wire from panel back to battery. The hot wire looked ok. The outside main fuse is spliced into the ground wire. – longtimealaskan Oct 16 '16 at 09:15
  • 1
    I´d say that you have a problem with your Reverse Battery Protection circuit. Best to go see a mechanic. – F. Bloggs Oct 16 '16 at 18:17