Headlight Troubles
 

Searched, and can't find something like this. Hopefully somebody has heard of something like this or can point me in the right direction.
Problem: Passenger side High beam does not work.
Attempt #1. Replace head light. Does not fix problem. Used a light I had laying around, so figure it may have been bad.
Attempt #2-5. Replace head lights with others, including a known working one. Still no high beam on that side.
Attempt #6. Get smart, and hook up voltmeter. 12 volts on connector on rear of assembly, through wiring, and into headlight connector. Start scratching head. Install headlight, no high beam.
Attempt #7. Measure 12 volts on headlight connector, until I plug in light. Then voltage goes to 0. Unplug light, volts goes to 12 again. Reinstall lights, and call it a day to go work on the house. This has got me :dizzy2:.
Suggestions? Now would be a good time for Euros? lol

Please explain how you measured voltage at the connector with the connector plugged into the headlamp?

Are you sure you measured the connector for the high beam? The low beam connector would also have 12V.

Sounds like you have a bad connection somewhere. Electrical power when idle will "float" at whatever voltage is on that circuit, under load, you pull a current draw and it causes the voltage to drop, usually not to a noticeable level, but, when you lose conductivity through a corroded or loose connection, you can't supply enough current flow to the device, which causes it to go into an undervoltage (brownout) condition, like trying to run your vacumm cleaner with a drinking straw on the end of the hose.
This could be a loose connector, corroded connection, or not likely but possibly an internally fractured wire. I would start by cleaning the connector, pop the back shell off of it and inspect the solder joints inside it, they often get powdery from moisture.

I don't believe you have a grounding issue in this case, as that would cause you to see full voltage all the time.

Brian, I have the connector that plugs into the headlight in my hand, with the + lead on the white wire's connector. I have the - lead on the battery ground. In my other hand is the headlight. I can barely plug in the light, and watch the voltage drop. The yellow wire I would believe to be for the low beam, since it has +12 volts on low beam setting and goes to 0 switched to high beam.
The connector does look a little green, so I'm gonna clean that when I get a chance. Last time I had the lights out I used the dielectric grease, so it could have corroded more since I had them out. They both did work since I've had the car.

The devil is in the details

Please confirm:

1) You get 12V when you check for voltage on the socket for the white wire with the socket removed from the bulb????

2) When you shut the high beams down, the 12V disappears from the socket with the white wire???

3) In order to check for voltage with the plug installed, you put the tip of the probe on the spade connector for the headlight???? Then you slide the plug onto the headlight connector and, with the probe still touching the spade connector of the headlight, the voltage now reads zero????

4) It's impossible to keep the probe on the socket while you are installing the socket...........correct???

If all four of the above are true..........you've got corrosion problems in the socket.

I had a problem like this with my parking lamps and it was that the wire inside of the insulation had virtually been reduced to a copper dust. It read 12v but everytime I plugged in the lamp it would not work. Replaced the forward section of wire and everything was OK.

Could be a bad ground too- if you are checking the voltage with the meter and touch carbody with the other lead instead of using the ground pin in the connector, you are bypassing the ground for that light.

Sorry to bring up an old thread, but I'd rather bring conclusion to this one than start another one.
Problem is solved. Removed fuse #7, cleaned the fuse and holder, reinstalled, and it's fully functional again. Like someone said, voltage was there, but couldn't support the current required for light operation. We had some reaction between dissimilar metals, though I can't remember what it's called now. Time to replace the vac pump, and I'll be rolling again.