Forum Discussion

Prober22's avatar
Prober22
Explorer
Aug 14, 2018

Fuse Blows on Bedroom Light Circuit

Hi Everyone,
My trailer is a 2012 Denali 265RL. About 4 years ago, when I would park in a new location, the 15 amp fuse on the Bedroom circuit would be blown when I got into the trailer. It was annoying. I just pulled the trailer out of the pole barn and the new fuse I put in blew immediately. The light in the pass through storage bay is on that circuit. I removed the fixture and unhooked it from the two wires.
There is no fuse in the panel now. With my multimeter, both wires complete the circuit while holding one probe on one wire and the other probe on the frame of the trailer.

If my electrical terms are not precise, go easy on me. I'm coach-able.
I think that the ground, or negative wire should cause the multimeter to buzz, while touching one probe to it, and the other probe to the frame. I think that the Hot, or positive wire should NOT cause the multimeter to buzz while touching a probe to it, while there is no fuse in place.

I think that the hot wire must be grounded to the frame somewhere. Does that sound correct? Given how the problem started out intermittently, and now is constant, I have this mental picture of the hot wire, at some point after it leaves the positive end of the fuse holder, being crushed against some part of the trailer frame, with damaged insulation. Does that sound reasonable?

Is there anything else I should check for before I start with trying to trace the problem?

My plan would be to disconnect all the power, remove the fuse panel from the wall, and then try to figure out which side is the hot side, and then start to trace that wire back to the bedroom lights, looking for damaged insulation on the wire.

Would the hot side wires be color coded differently than the ground side wires?

I would really appreciate any tips on how to fix this problem. Is there a way to test certain, unaccessible sections of the wire? Is it best to start at the fuse end on the wire and work toward the lights, or the other way around.

I am Twittering with excitement.
Thanks,
Jeff
  • enblethen's avatar
    enblethen
    Nomad
    Aug 14, 2018
    Locate all the lights on the circuit and remove the bulbs. It is possible that some one put in the wrong type of lamp shorting the circuit in the lamp holder.
  • azrving's avatar
    azrving
    Explorer
    Aug 15, 2018
    If the light in the bedroom only has the hot and negative going to it back up to the light in the cargo area and remove it. It's common to have wiring problems where the connections are made yes it could wear through somewhere and rub but it's common to have problems where they connect to the lights. If the cargo area light has doubled wires feeding it then you know that two of those wires are probably going on to the bedroom and the other two might be coming from the power or they're going to another light. Identify the light on the end of that run because that's the light that will only have one hot and one negative it's at the end of the string try to work your way backwards from there. Again it's more likely to have the insulator at the base of the bulb cracked or deteriorated or something shorted in the light area. Figure out how many lights you have on that string
  • Prober22's avatar
    Prober22
    Explorer
    Aug 15, 2018
    Hi,
    Thanks,
    The light in the cargo area has the single wires, so it must be at the end of the line. I have the three ceiling fixtures in the bedroom hanging free from the deiling. They have the double supply wires.
    Do you think I should disconnect those from the wires and then put a fuse in and see what happens? That would eliminate the light fixtures as the cause, . . . Correct?
    Jeff
  • enblethen's avatar
    enblethen
    Nomad
    Aug 15, 2018
    You can test using an ohm meter.
    Go to mid point of what you think is the center of the circuit. Cut it open there. Test from the fuse panel to see if positive is showing resistance. Take lamps out for good reading.
    Are there separate switches on the light fixtures? Make sure they are off for first test, then turn on and see if reading changes. this should isolate area of problem.
    Is there a vent in area? If so that could have been wired for fan. Can check by removing garnish. Wires are usually tucked in ceiling.
  • azrving's avatar
    azrving
    Explorer
    Aug 15, 2018
    Remove all the bulbs and try it. Then look closely at each socket because the little contacts short out sometimes. You might get an idea of how they ran the wiring from the Power Center to the first light and on down to the last one and maybe remove one light at a time.
  • azrving's avatar
    azrving
    Explorer
    Aug 15, 2018
    If you were to put a 12 volt bulb in place of the fuse and the system has a short in it you will see the bulb illuminated. With it illuminated try working through the string until the light goes out. I had a fan wire fall out of the wire nut and touch the frame. You could have a bad bulb, broken bulb socket, wires rubbing in socket, wires popped out of wire nut or wire shorted to frame.

    Have you or anyone done any other work on the rig before this problem showed up? Did you install anything like coat hook, shelf, anything?
  • david_iona's avatar
    david_iona
    Explorer
    Aug 15, 2018
    Had a similar issue with an 05 Cardinal. I traced wires, tightened connections, secured connections in tbe 12 volt panel. This went on for a few years with me buying 15 amp 12v fuses in bulk. Then one evening I went out to get something out of the street side bay and my wife said the lights just flickered when I opened the bay door. I closed it and opened if again and the bedroom lights flickered. I was watching the cargo door as I lifted it and the door touched the underside of the bedroom slide and sparked at the point the two metal trims touched. It blew the fuse that time. I could nevet find the ground point that caused the short but I put a strip of black elec tape at tbe point of the spark and never blew another fuse up to the day I sold the fifth wheel. And yes, I told the new owners about it and left the dozen or more 15 amp fuses with them..
  • BB_TX's avatar
    BB_TX
    Nomad
    Aug 15, 2018
    As far as measuring with your multimeter. Remember that a standard light bulb is nothing more than a relatively low resistance wire (the filament) connecting hot to ground. Two bulbs in parallel would measure half that resistance. Three = one third. Etc. So you will measure some continuity to ground from the hot wire with the bulbs still in the sockets. To check for no continuity you need to remove all bulbs in that circuit.
  • Executive45's avatar
    Executive45
    Explorer III
    Aug 15, 2018
    My guess is a bad switch. Often they'll short within themselves and you won't be able to tell. Remove the lights one at a time and see which one is causing the trouble...Good luck...Dennis

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