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EFV-8 Club Forum / General Ford Discussion / Crazy headlights??

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Discussion Topic: Crazy headlights??

Barney

12-25-2021 @ 5:20 PM

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Merry Christmas; I trust Santa treated you better than you deserved.
I have an electrical issue that has me somewhat baffled, or maybe I'm just a dunce.
1940 Ford, standard, 6 Volt w/ positive ground:
With headlamps removed - Light switch pulled to 'on', low beams selected, voltage measured at headlamp plug from low beam terminal to ground = 6 volts. Voltage measured from high beam terminal to ground = 0 volts. Now with high beams selected, voltage from low beam terminal to ground = 0. Voltage measured from high beam terminal to ground = 6 volts. Makes perfect sense to me.
Now - with new Wagner, sealed beam headlights installed: With low beams selected, voltage from low beam terminal to ground = 6 volts. Voltage from high beam terminal = approx 4 volts. With high beams selected, voltage from low beam terminal to ground = approx 6 volts. Voltage from high beam terminal to ground = approx 6 volts.
My understanding is that the "jewel light" should be illuminated only when high beams are selected, and it operates that way when the headlamps are not installed. But when they're installed, the jewel light is on when either low or high beams is selected. However, the light is very noticeably dimmer when low beams are selected. Actually, this could be a nice reminder feature so as to be a reminder that headlamps are on when the car is shut down. Looking at the headlamps - they seem to operate in a normal manner. I'm concerned that voltage is going to both the low and high beam terminals simultaneously.
Any thoughts?
Barney
PS Sorry to be so wordy.

JayChicago

12-26-2021 @ 8:42 AM

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Sounds to me like resistance in the ground side of headlight.

Bulb’s low beam and high beam circuits share a common ground terminal. If current going to ground cannot easily get all the way back to the battery, voltage will back-feed into the other circuit.

Barney

12-27-2021 @ 3:36 AM

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Good morning, Jay,
Thank you for your explanation. It appears you hit the 'nail on the head'. I know proper grounding is very important with these old machines and thought I'd accomplished that. I searched for a bad ground and found a loose connection in a hidden area. It didn't totally fix the issue, but made a noticeable difference. Apparently, current is jumping between the low and high beam terminals in the headlamp as you diagnosed. I'll keep searching for more grounding problems; I'm convinced I'm on the right track, thanks to your great explanation.
Barney

Barney

12-27-2021 @ 3:50 AM

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Jay,
BTW, I measured .4 ohms (yes, point four) ohms across the low and high beam terminals - the same on both new Wagner (made in China) headlamps. I used a Simpson model 467 true RMS digital multimeter, not a cheapie. Knowing just enough about electricity to be dangerous, I would have guessed the resistance across those two terminals should be infinite / open.
Barney

40 Coupe

12-27-2021 @ 5:20 AM

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0.4 ohms sounds OK. If the resistance was infinite the lights would be open circuit. Headlights use a lot of current so the resistance should be very low. Your problem does sound like two different problems. I also suspect there is a ground problem but also suspect a problem with the foot dimming switch. If you connect a test wire from a good ground point to the wire for the headlight ground and recheck. Even try to connect the test ground to the back of the headlight bulb since the short harness could be bad on the ground wire. The symptoms you described above happen to both headlights at the same time???
With power to the driving beam there is no way the dash high beam light should illuminate unless the foot switch is bad.

Barney

12-27-2021 @ 6:08 PM

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Mr. 40Coupe,
Thank you for sharing your thoughts. You and Jay seem to agree that I have a ground problem. Jay led me to one ground problem, but I'm betting there are more as the condition is better but not 100%. 40Coupe, you mentioned the dimmer switch. It's brand new (probably chinese), so I didn't suspect it. I don't recall a ground wire being attached to the switch base; I gotta check. I certainly can't rely on a ground connection through the floorboard because that's what it is - a board! Thank you much. I'll check it out, but probably not until the new year.
Happy New Year to All,
Barney

40 Coupe

12-28-2021 @ 5:12 AM

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Barney: I suspect a problem with the foot switch because the switch should isolate the country beam and the dash indicating light when just the low beam lights are ON. Possible the switch, if new, is not wired correctly. It has a common terminal which you have to find, That common is wired to the power input to the lights. The other two terminals should never have continuity to each other. Check the schematic diagram.

JayChicago

12-28-2021 @ 12:43 PM

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40Coupe

What about my theory above?
The low beam circuit and the high beam circuit DO have a common point: the shared ground terminal on the light bulb. If low beam current cannot easily get to ground there, it can back feed into the high beam circuit and go to ground thru the dash indicator light bulb.

Cannot rule out a problem with the foot switch. But I don't think the symptoms necessarily point to it. Yet.

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