Should there be voltage across the high beam and low beam terminal?
 

The headlights on my 1936 Ford pickup had been converted to sealed beam halogens. Wires coming out of the switch at the bottom of the steering column were dead ended. A headlight switch was mounted in the dash. Only the ground wire and the low beam wire were connected to the headlight. I connected the high beam wire and installed a floor mounted dimmer switch.

There are 12 volts when the ground lead is connected to the ground wire with the positive lead connected to the high beam (with the dimmer switch on high beam), and there are 12 volts when the positive lead is connected to low beam (with the dimmer switch on low beam).

However, checking across the high beam terminal and the low beam terminal, there are 12 volts (when the dimmer switch is on high beam) and there are 3.6 volts across the high beam and low beam (when the dimmer switch is on low beam).

Should there be voltage across the high beam and low beam?

I am not sure if this is okay or if the headlights are not wired correctly.

I appreciate your help.

Re: Should there be voltage across the high beam and low beam terminal?
 

Sounds normal to me. The side that is not energized is providing a ground path for the volt meter through the bulb from the energized side.

Re: Should there be voltage across the high beam and low beam terminal?
 

The voltage (current) goes through the filament in the bulb to ground and eventually back to the battery. So, there is current (and voltage potential) in the grounds and grounds tend to back feed through other connections. They may or may not be wired correctly, are they working ok?

Re: Should there be voltage across the high beam and low beam terminal?
 

I appreciate the information.

I installed the headlights and both the high beam and low beam are working okay.

Thanks again!

Re: Should there be voltage across the high beam and low beam terminal?
 

Your answer makes perfect sense. I wasn't thinking of it in those terms.

Re: Should there be voltage across the high beam and low beam terminal?
 

I ran into the same situation where the 'leakover' voltage from the headlight bulb high to low beam terminals caused the red dash high beam indicator was lite in both high and low beam positions.


The fix was to change to Sylvania H6024 bulbs. They do NOT have a connection between high and low beams.

Re: Should there be voltage across the high beam and low beam terminal?
 

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AND....ya gotta keep in mind that a volt meter does not NECESSARILY measure voltage. More realistically, it measures voltage DIFFERENTIAL between two points. You can have a thousand volts at a particular connection. But place BOTH meter probes on that SAME electrical point, and your meter will show 0.0v (zero volts)....DIFFERENTIAL. I'm just saying that one must remain fully-aware of exactly what it is that you are measuring. But what do I know? DD