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Dome light conundrum - need help

Interior and Electrical

  1. shadango

    shadango Well-Known Member

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    We are trying to patch in two extra courtesy lamps we mounted under the dash in the 80 Volare.

    I figured we would just power them by the wire that feeds the dome lamp...so they come on when the door opens, off when closed.

    Easier said than done apparantly.

    The diagram shows a pink and a yellow wire going to the dome light. And of course the lamp grounds to the door pins. I figured one of the two wires -- pink and yellow -- would be the right one....

    We located the pink and yellow wires in the plug behind the driver side kick panel.

    One wire is hot the whole time

    The other wire is hot when the door is CLOSED and goes dead when the door is open.

    WHAT THE HECK. If I tie into the one thats always hot, the lights will be on at all times. The other, they will be on when the doors are closed but go out when opened. What are we missing? I thought for sure ONE wire would work.

    The lights we are using under the dash get their own ground from their mounts.

    So the only other way I can see to do this is use light units that are not grounded by their mounts (two wire) and wire the pink to one side and the yellow to the other.....but how does that even work???

    Ist here maybe a ready-made wire under the dash somewhere that would feed courtesy lights that were not included on this car?
     
    Last edited: May 12, 2018
  2. Justwondering

    Justwondering Well-Known Member

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    Do you have anything that lights the glove compartment or anything in the door panels?.

    My Fifth Avenue has a vanity light in the passenger visor... I must admit I don't know much about the Volare wiring.

    JW
     
  3. Aspen500

    Aspen500 Well-Known Member

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    The only way I can see that it'll work is to use lights with ground wires. Hook the power feed to the pink wire (fused B+ to dome lights) and then the ground to the yellow wire. There is no circuit, that I'm aware of, which is powered only when the door is open.
     
  4. Cordoba1

    Cordoba1 Well-Known Member

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    So what is happening is this: The whole circuit is "hot" or live all the time. Battery + > Light Bulb(s) > Door Switch > Door switch closes to ground (-) when the door is open. So... With the door closed, you will read battery voltage on your meter. The voltage is flowing through the bulb to your meter. If you short that wire to ground, the dome lights will illuminate. To add more lights, wire one half to always-hot wire, and the other light terminal to the wire that appears to go hot when the door is closed. This wire is effectively the ground. Using this method, you'll be adding a light in parallel to the others. Make sense?
     
    Last edited: May 12, 2018
    4speedjim and shadango like this.
  5. shadango

    shadango Well-Known Member

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    Thanks...yeah that is where I was guessing it might have to go. Though I still dont understand the principle behind it.....if voltage is flowing thru the bulb to my meter how is it not illuminating? When we checked for voltage as I noted above it was from the harness side coming from the dash.....the one that goes hot when the door pin is OPEN is what doesnt make sense to me....

    I hate electrical stuff. LOL

    The previous owner had bolted some lights into the footwells of the car.....like this one except clear plastic. They were bolted onto metal and wired together but never connected to hot. Now I know why. LOL Guess we have to use different style lights....no way to isolate that bracket (the ground) that would be safe to connect it the way it needs to be connected........right?.

    73811_Z1.jpg
     
  6. Cordoba1

    Cordoba1 Well-Known Member

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    You can use a light like that, just isolate the mount from ground. You could perhaps mount the light to the plastic kick panel. Run the attached wire to an always hot source, and then attach a wire to the mounting tab and run that to the wire that goes to your door switch.
     
  7. kkritsilas

    kkritsilas Well-Known Member

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    Shadango:

    You have voltage, but you don't have a complete circuit.

    The circuit is hot (+12 V, say pink wire) through the dome light bulb, and over to the yellow wire that goes to the dorr pin switches. With the doors open, the yellow wire is grounded, and you have a complete circuit, as current flows from the pink wire, the dome light bulb (causing the light bulb to light up), onto the yellow wire, which is grounded by the door pin switches. When the doors are closed, the door pin switches are no longer connected to ground. This stops the flow of current, so the dome light has no current flowing through it, and the dome light is off.

    Voltage only shows that there is voltage present, not that there is a complete circuit. You are seeing voltage on your meter because, with the doors closed, the yellow wire is "floating"; without a ground. Because there is no current flow, there is no voltage drop across the pink wire, dome light bulb, or yellow wire. with the doors closed, your circuit is not complete. your meter will see pretty close to battery voltage.

    A complete circuit requires a source (12V Battery or alternator in a car), and a ground (or return as it is sometimes called, or battery negative in a car). If you hve both, you have a complete circuit. Doesn't matter what is being powered by the circuit; you must have a source, and you must have a ground/return, or current will not flow. Current is what actually does things, not voltage.
     
    4speedjim and Justwondering like this.
  8. 4speedjim

    4speedjim Well-Known Member

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    Yep yep... You've got to have a complete circuit for anything electrical to work. European cars where always positive ground. Not sure about modern EU cars but pre 70's were all wired like that. It was confusing
     
    Last edited: May 17, 2018