If 14 gauge wire can supply 120 volts to three 60 watt light bulbs

Then why do some vehicles require 3 power wires for one light bulb ( 2 for HID lighting for the ballast and one for the parking light ) with 2 grounds, couldn't they just use one ground and one supply that could hold the current, then split at the connector for the internals ?

  • You do realise that a 60W bulb will draw 0.5A at 120V, so three bulbs would draw 1.5A. At 12V on a car, a 60W bulb will draw 5A, therefore 3 together would draw 15A.
    – HandyHowie
    Aug 28, 2023 at 7:13
  • Can you point out a car schematic where you see one supply and 2 grounds for the same bulb, so that I can see what you mean?
    – HandyHowie
    Aug 28, 2023 at 7:15
  • 2011 ford edge. Sep 1, 2023 at 8:33

1 Answer 1


DC current flows from negative to positive. The starter only needs one large gauge red wire from battery positive, ground is via battery negative to chassis and engine block. The alternator only needs a fusible link wire for power, fused to blow around 25 amps or more That's input power from ground. Output power is thru frame ground to supply all the electrical needs of a vehicle while recharging the battery, anywhere from 125 amps to 250 amps plus for heavy duty trucks and police vehicles. Ground is where current flows. HID lights requires two wires; the ballast starting current can jump to 10 amps+ momentarily then drop back to running current, approximately 3 amps or so. A a separate power wire to parking lights still uses a separate ground to the chassis so lighting won't dim when hid lights startup. DC circuitry can be complicated and I'm still learning about it myself.

  • 1
    Why have you mentioned that electrons flow from negative to positive? Everyone in general uses conventional current, flowing from positive to negative. Talking about electron flow just confuses things.
    – HandyHowie
    Aug 27, 2023 at 21:54
  • One example to point out electron flow; examine your alternator wiring. See any 125-250 amp wire gauge connection between alternator and battery? Until you accept dc current flow as opposite to voltage flow, you'll never explain how alternators output.
    – F Dryer
    Aug 28, 2023 at 2:49
  • 1
    Current flows in a loop, if you have 100A on the ground connection of the alternator, there is 100A on the positive terminal of the alternator. You can’t have more current on one side than the other. If that is what you think is happening, then you are not understanding something. It doesn’t matter which way you imagine the electricity flowing either. It can be AC or DC. The current is always the same. If you had several wires on one terminal, then the 100A can be shared between them, but it would add up to 100A.
    – HandyHowie
    Aug 28, 2023 at 6:54
  • Incorrect. the 'hot'wire to power the alternator is a fusible link. It is not fused for 100 amps. Examine any hot wire to alternators and tell me the gauge wire is 8, 6 or 4.......... Perhaps reviewing how alternators operate may enlighten you.
    – F Dryer
    Aug 28, 2023 at 19:07

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