Halogen Headlights

Discussion in 'Classic Mustang Specific Tech' started by candphall, Jul 4, 2013.


  1. candphall

    candphall Member

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    This is what I found , the car has been totally rewired , the voltage out of the headlight harness is 12.30 volts. When I plug in the headlight extensions the voltage drops to 11.58 volts at the bulbs. I am attributing the voltage drop to old extensions which I have not replaced. Hence the dim lights. Am I thinking correctly. I would like a second opinion before replacing the extensions. The only thing I find odd is the voltage a drop is identical on both sides.
     
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  2. 66Coupe289POWER

    66Coupe289POWER Member

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    [​IMG]
    Please forgive my crude diagram, paint is not my strong point. This is a overly simplified diagram of the headlights. All voltage drop readings need to be done with the headlights on. First measure voltage from point A to point J to check the ground side. You want as close to 0v as possible and anything over 0.5v is not good. If you have a lot of drop, isolate where by measuring from point A to point K, point J to point L, and point K to point L. Clean connectors, replace loose connections, solder twisted wires, or whatever else you need to do to repair the circuit. Next when the ground is good measure from point B to point C, point C to point D, so on and so forth until you have checked every leg of the circuit and repair as needed. If there is drop between C and D or E,F,and H then that switch is worn out. Remember this is a series circuit and anything that has resistance will use some voltage and that reduces the voltage to the lights.
     
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  3. tx65coupe

    tx65coupe Active Member

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    It would be helpful to have all the info in one thread instead of making a new thread each time.
     
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  4. candphall

    candphall Member

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    Thanks. And no more new threads, got it
     
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