Voltage on 12v circuit with no fuse?!

Discussion in 'Wiring' started by mausmobile, Jul 17, 2019.

  1. mausmobile

    mausmobile New Member

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    Hi everyone-

    Problem in brief:

    While troubleshooting my camper's electrical system, I discovered a circuit that has 8 volts on it at all times, even with the fuse pulled. In fact, it gets 8 volts even with ALL the fuses pulled out of the converter panel.

    The full story:

    Behind my refrigerator, I have several pigtail connectors coming from the converter panel that can be pulled apart to allow different sections of the camper to be swapped in to different power circuits. When I acquired the camper, the emergency trailer breakaway switch did not work. I discovered it was plugged into a fused circuit that was only getting 8 volts - no wonder it didn't work.

    I located the circuit with constant unfused 12v power from the panel and plugged the breakaway/brake system into that. Breakaway now works exactly as it should. I believe this is where it is supposed to be plugged in, and perhaps the pigtails were swapped by a previous owner. However, the ceiling lights in the front half of the camper, which WERE plugged into the constant power pigtail, now need to plug into one of the fused circuits. The only one left is this strange 8V line.

    In the course of mapping out the circuits, I pulled every fuse out of the converter panel. The 8v circuit STILL measures 8 volts, even with all the fuses pulled. And of course I need 12 volts for my lights.

    1) HOW is it even possible for a circuit to have voltage even with all the fuses pulled, and if there is a short, why is it only getting 8v instead of 12v?

    2) How can I troubleshoot/locate the issue so I can have normal 12v on this circuit to power the lights?

    Thanks for your help,
    mausmobile
     
    Last edited: Jul 17, 2019
  2. rabird

    rabird Howdy!

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    The 'convert' won't have power in transit, a brake away should be connect directly to the battery.
     
    Raycfe likes this.
  3. mausmobile

    mausmobile New Member

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    Thanks! My camper is actually wired this way from the manufacturer. The battery runs to the converter panel before it goes anywhere else. The breakaway has its own set of wires that run from the tongue to the rear of the camper to connect with the brake system and power source. I have tested the breakaway switch with the camper disconnected from the tow vehicle and the brakes lock up properly.

    I've solved the breakaway problem, which I only described to give background. I'm now looking for help with the 8v circuit issue.
     
  4. eoleson1

    eoleson1 Well-Known Member

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    Have you checked the ground on the breakaway circuit?
     
  5. Raycfe

    Raycfe Waterford Ct.

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    The breakaway system doesn't have a ground circuit, It only provides power to the brakes ...... and in my book should be connected directly to the battery positive terminal.
    Your 8 volt problem is a (high resistance) causing the lower voltage. Usually a bad connection ..... or some type of load in the circuit.
    Start at the battery (trailer unplugged from shore power)..12 across battery> move the meter ground connection to the frame on tongue, should be the same >with a long wire move the meter ground connection to the ground connection at the convertor, should be 12 volts. There are other was to check the circuit but this my way. If all these tests are the same reading the ground circuit is good. Now do the positive side> after battery terminal do output of circuit breaker> 12 volts at the convertor. If tests are same feed is good.
    Now your 8 volt circuit .......... Make sure your meter have a known good ground connection and as you measure the 8 volt circuit start to unplug things ...... furnace . then water pump . then the refrigerator to see if the circuit changes or go dead.
    How many fuses do you have in your convertor? My old Jayco only had one, so I added small automotive fuse box to feed my added circuits that ran off the battery.
     
  6. brwarrior

    brwarrior Active Member

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    Does your 12VDC fuse panel have LED blown fuse indicators? If so that could be the source of your low voltage with fuses removed. They let a little voltage through but hardly any current is available.

    I'm with Ray in that the breakaway should be on a direct, unfused line from the battery.
     

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