Which One is Hot?

Discussion in 'Miscellaneous Repairs & Maintenance' started by hayyward, Jun 15, 2019.

  1. hayyward

    hayyward Active Member

    Messages:
    238
    Likes Received:
    110
    Joined:
    Sep 16, 2006
    Location:
    Packerland
    We're attempting to install a 12v USB charger, tapping into the kill switch wires (because they're accessible). Thing is, both wires are black, both have writing on the wire casing and there are no distinguishing marks on the terminals. While manually depressing the switch, we've tried 3 different types of volt meters and get no readings at all from any of them. Lights are working when the switch is depressed so we know the circuit is live. How can we determine which wire is hot? What are we missing?
     
  2. SteveP

    SteveP Well-Known Member

    Messages:
    1,311
    Likes Received:
    313
    Joined:
    May 21, 2015
    It shouldn't matter. When the switch is depressed both are hot. And you're not likely to be charging anything in the camper when the galley is folded.
     
  3. hayyward

    hayyward Active Member

    Messages:
    238
    Likes Received:
    110
    Joined:
    Sep 16, 2006
    Location:
    Packerland
    Thanks for your prompt reply. So you're saying that the hot from the USB charger can go to either of the black wires from the kill switch and the ground from the charger can tie into any metal thing to ground?
     
  4. SteveP

    SteveP Well-Known Member

    Messages:
    1,311
    Likes Received:
    313
    Joined:
    May 21, 2015
    Thjere should be a white wire nearby you can tie into.
     
  5. roybraddy

    roybraddy Well-Known Member

    Messages:
    2,065
    Likes Received:
    702
    Joined:
    Mar 23, 2016
    Location:
    King George, Virginia
    One of your multimeter leads should go to the NEG side of the Battery source or frame ground perhaps… The Positive would go to either one of those black wires... Just keep in mind your project will not have power if the switch is open when the kitchem is in fold over position. I would determine which is always hot and use that one...

    I don't know if I would mess with those wires to the ceiling disconnect switch. They are doing a big safety feature for you preventing the interior lights from coming ON when your roof is down to get something from getting too hot and start a fire...

    If it was me I would find another ALWAYS ON 12V source ...

    Being a COMMS guy I am always hooking something up haha .. I ran out of available 12VDC circuits from the 12VDC Distribution Panel along time ago... I installed one of those Blue Sea SUB Panels (AMAZON) that will give several spare FUSED 12VDC sources... I also like to use this two conductor 'BOAT CABLE" for my wiring... Carries both + and - 12VDC conductors...


    [​IMG]
    Google image

    For me it was never a good idea to tap into some other already used 12VDC circuit. I would blow the fuse for sure sooner or later and forgot where and what I was taped into haha...

    Roy Ken
    [​IMG]
     
    nineoaks2004 likes this.
  6. hayyward

    hayyward Active Member

    Messages:
    238
    Likes Received:
    110
    Joined:
    Sep 16, 2006
    Location:
    Packerland
    Surely the USB port will not be in use while the camper is down but I get what you're saying about not messing with the kill switch. There are a couple other wires coming in near there from the porch light. Both wires are white but one must be hot, right? We might be able to tie into those without having to contort our bodies too much. (Add bifocals and we're almost dysfunctional in these tight areas!)

    This device has an inline fuse, we weren't sure if we needed to keep that or not since the whole circuit is on a fuse at the box. The fuse box is full so can't add anything there, and to access that electrical area would require some cabinet deconstructing.

    This is way more complicated than we expected. :confused: Good thing we haven't drilled any holes yet.
     
  7. rabird

    rabird Howdy!

    Messages:
    6,546
    Likes Received:
    247
    Joined:
    Mar 3, 2006
    Location:
    TX
    yes.

    use your volt meter (set to DC 0-20 scale) to probe (red probe) one black wire and probe (black probe) the frame of the trailer, one black will be always be 'hot' and the other will be hot when the button is pushed. As mentioned the white wire(s) that come from the 12v side is 12v neg (same as frame).

    I found easy access near the back of the converter, the converter comes with several short 12v+ and mine were wire nutted to circuits, undo and add the wire.
     
    hayyward likes this.
  8. hayyward

    hayyward Active Member

    Messages:
    238
    Likes Received:
    110
    Joined:
    Sep 16, 2006
    Location:
    Packerland
    The problem we had with the volt meters was that the negative we touched with the probe was not a frame member. Once we did that differently (correctly) we got a reading. We ended up using the kill switch wire that is not always hot and tied into the porch light ground. We now have a working 12v USB charger!

    Thanks you guys for the assist. I'm always impressed by the deep and varied knowledge of the portal members.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.