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  1. #1
    Left The Driveway
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    Unhappy 15 Amp 12 V fuse randomly blows w no activity (or not)

    Bob and Katy C
    2017 Solitude 310GK purchased used in 2021
    2011 Ram 2500 w B&W Companion

    Original owner said "there is an electrical leak - carry some 15 Amp fuses". (I have a bag of 50). Circuit controls 12 V control signals to Heat Pump, Refrigerator, Gas Furnace, includes Thermostat and CO/Propane detector plus 2 LED lights near refrigerator. Frequency of fuse blowing varies from "immediate and repeated" to up to 2 months and everything in between. Will blow when nothing is being used, trailer static, no wind blowing or occasionally when traveling. Has been known to not blow all the way from Seattle to Phoenix and back but then to blow repeatedly (4 in rapid fire sequence) while camped. In that case, let it just sit for three hours and new fuse then worked fine for 6 hrs. but could not keep it operational at all for the next several days while traveling (no Refrigerator and no Furnace in late October). Since then, . . . . Will blow with Shorepower connected only, battery power only or both connected. Have replaced Thermostat and disconnected CO/Propane detector. Fuse still blows randomly but it lasted for 2 months after Thermostat replacement. Meanwhile, varied using Heat Pump, Refrigerator and Furnace in various combinations and none at all. Fuse finally blew with nothing operating except the Thermostat for no apparent reason. Have used Clamping Ampmeter but never more than 1.4 Amps with everything running. Tried moving circuit to a blank location on the fuse panel. Didn't help. Currently tearing into Furnace to look for a potential short. Any thoughts?
    Last edited by Bob Chamberlin; 01-16-2023 at 04:27 PM. Reason: new thought. Have never found rodent dropings or chewed wiring or surfaces.

  2. #2
    Site Team Ynot4me2's Avatar
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    Those are hard to pin point and find. Sounds like either a loose wire or frayed. Is it always the same 15amp fuse that's blowing?
    Steph & Lise
    2019 F150 Lariat 2.7 EB
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  3. #3
    Left The Driveway
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    Thank you so much for your very quick response. It is appreciated. Yes, there is only one 12 V circuit that has a problem. (Always the same fuse slot.) Have opened the Furnace (which was very dirty). Vacuumed and cleaned it all out and found a frayed wire next to a metal structural member. Re-routed the wire and covered it with heat-shrink tape. All working fine but based on history this may not be a fix. The problem has NOT been consistent and has been known to happen randomly when nothing was moving in the trailer and no appliances were running. That does not mean that the Furnace was not trying to come one when the fuse blew so I will have to just wait and see. Thanks again for responding.

  4. #4
    Site Team xrated's Avatar
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    Quote Originally Posted by Bob Chamberlin View Post
    Thank you so much for your very quick response. It is appreciated. Yes, there is only one 12 V circuit that has a problem. (Always the same fuse slot.) Have opened the Furnace (which was very dirty). Vacuumed and cleaned it all out and found a frayed wire next to a metal structural member. Re-routed the wire and covered it with heat-shrink tape. All working fine but based on history this may not be a fix. The problem has NOT been consistent and has been known to happen randomly when nothing was moving in the trailer and no appliances were running. That does not mean that the Furnace was not trying to come one when the fuse blew so I will have to just wait and see. Thanks again for responding.
    The location that you found the frayed wire......did you see any signs of arcing in that area? If that was it, as many times as you have replaced the 15A fuse, there would definitely have been blackened spots where the wire arced repeatedly.
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  5. #5
    Site Sponsor
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    A trick from the old days that can help locate loose or intermittently shorted wires is to use an AM radio. Tune it to a space where there is no station. Jiggle, shake, pull etc. on any wires or components connected to or near the suspect wire. Electrical arcing produces strong, broadband RF signals and the radio will produce a sound similar to the way lightning did back when people listed to AM. It can be a great tool to narrow down a mystery problem.
    John & Kathy
    2014 F250 Lariat FX4 6.2L SBCC
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  6. #6
    Big Traveler
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    Well after examining all the wiring I could...I would buy a package of fuse holders and fuse everything at 5 amps. If the 15 still blows, it's in the supply wiring. If a 5 blows...you know where the issue is.
    2018 Dodge 3500 6.7 Cummins SRW w/Aisin
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  7. #7
    Rolling Along
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    Never more than 1.4 amps with a clamp on begs to ask why a 15 amp protector? I would rig up an inline multimeter for amps with some extension wires and alligator clips. Then start turning things on and watch the amp meter. Bang doors and roof panels and jiggle your 12V appliances and systems on that leg. I would think the 2 LED lights would draw more than 1.4 when on. Are they puck style?
    Randy and Kris

  8. #8
    Seasoned Camper
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    Quote Originally Posted by Scott'n'Wendy View Post
    Well after examining all the wiring I could...I would buy a package of fuse holders and fuse everything at 5 amps. If the 15 still blows, it's in the supply wiring. If a 5 blows...you know where the issue is.
    @Bob Chamberlin I’d do what @Scott’n’Wendy says. I use this on grain drying LP heaters to find bad components when I get a frustrating intermittent fuse blowing issue. Works good.
    Larry and JoAnna
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  9. #9
    Seasoned Camper
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    Quote Originally Posted by stroguy View Post
    Never more than 1.4 amps with a clamp on begs to ask why a 15 amp protector? I would rig up an inline multimeter for amps with some extension wires and alligator clips. Then start turning things on and watch the amp meter. Bang doors and roof panels and jiggle your 12V appliances and systems on that leg. I would think the 2 LED lights would draw more than 1.4 when on. Are they puck style?
    Not a bad idea but the fuse will probably blow quicker then the meter reacts.

    I suggest connecting a 12v incandescent light (old school taillight) in place of the fuse. Then bang shake move everything you can. The light may be on an dim until you trigger the short, then it will be bright. The more you can trigger the bright bulb the closer to the issue.

    Of course hopefully the wire you found by the furnace is the issue and you are done.
    2021 Imagine 2800BH
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  10. #10
    Site Team traveldawg's Avatar
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    I’d be separating out some of those loads onto their own circuits. It sounds to me like a lot of loads for one circuit. Similar to the 15 amps GD provided up to my control panel for soooo many things. Onc e I split the loads onto 2 circuits - no more issues.
    Larry KE4DMG
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