Headlight wiring issue

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Model T Ford Forum: Forum 2016: Headlight wiring issue
Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Green - So Cal on Sunday, December 25, 2016 - 10:46 pm:

I have an issue with phantom voltage occurring at my headlight connectors on a 1924 stock setup. With the connectors disconnected from the headlight bucket, I read 6.3V on one wire (normal) and simultaneously 2.0V on the other (abnormal) on each of the left and right connectors. The voltage alternates between the wires when the headlight switch is moved from the DIM to ON positions. Both the right and left light connectors exhibit the same voltage readings and behavior.

Perhaps the issue is in the main headlight switch? I hate to have to tear apart that switch!

Anyone else have a similar problem or suggestion?


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Menzies on Sunday, December 25, 2016 - 11:27 pm:

Disconnect the wire from the switch and test, maby the leakage is through the cloth insulation.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Monday, December 26, 2016 - 07:33 am:

I helped a guy with a similar problem last year.

He had a Bright/Dim correct dual bulb on one side and a single element magneto bulb on the other side.

One bulb was rather dim and very confusing to him.

Changing that magneto bulb made everything right.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Dupree on Monday, December 26, 2016 - 07:58 am:

Bad ground

Ron Dupree


Top of pagePrevious messageNext messageBottom of page Link to this message  By Carl Sorenson-Montrose,CO on Monday, December 26, 2016 - 08:52 am:

Like Ron Said.........Bad Ground...


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Monday, December 26, 2016 - 08:56 am:

It is probably normal. You are trying to measure low voltage with a digital meter. You will come up with goofy stuff that doesn't make sense.

You should troubleshoot 6V power and ground problems using a light bulb to eliminate false readings.

Question: Is there any problem when the wires are connected as Ford wiring diagrams show?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Green - So Cal on Monday, December 26, 2016 - 12:06 pm:

Royce was partially right; but I was using an analog meter. After testing and tracing all headlight & tail light wires, it turned out that they were not wired as per Ford diagram. I determined when each of the wires was hot (Dim, Bright & tail) when they should be as per the dash switch position. After that there was no voltage bleed between the two contacts at the headlight buckets.

Additional question: On the headlight thimble connectors, is the TOP position for DIM (and the BOTTOM position for BRIGHT)?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Monday, December 26, 2016 - 12:13 pm:

The bulb does not have staggered pins so after the bulb is installed correctly with the offset filament to the top(dim) you see which wire lights it up when the switch is set to dim. Yes to your question.


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