Headlight electrical question, bad ground Options

[vin man]

On the driver side of my 71, the low beam comes on, but just barely. High beam works fine (Both beam are good on passenger side).

I have replaced the bulb, but still have the issue. While I suspect a bad ground, if that was the case, wouldn't the high beam not work properly has well?

According to electrical diagram, there is only one ground wire coming out of the headlight.

Anyone have advice on how to troubleshoot? I've checked the ground connection at the body and it is good.

Thanks.

[Dave_Darling]

What kind of voltage are you seeing across each filament?

Is it possible that the low beam is grounding through the high beam rather than through the ground wire? Are the wires plugged in correctly?

--DD

[vin man]

What kind of voltage are you seeing across each filament?

Is it possible that the low beam is grounding through the high beam rather than through the ground wire? Are the wires plugged in correctly?

--DD

I'm no expert, but I suspect that the situation is exactly as you describe. It is not grounding properly, but instead through the high beam.

How would I measure the voltage through the individual filaments? Would that be take reading on yellow wire and ground, then white wire and ground?


The low beam does come on, but very very faint.

[Dave_Darling]

That's how you'd do the measurement.

--DD

[jcd914]

Compare the wires on each headlight bulb. The white and brown wires are probably connected differently on each headlight.

Jim

[vin man]

That's how you'd do the measurement.

--DD

Will check tonight.

Compare the wires on each headlight bulb. The white and brown wires are probably connected differently on each headlight.

Jim

I had a similar thought. This is quite likely the problem as when the PO put the headlights in, he did not use a plug but just 3 separate connections to the socket. While I just pulled and replaced, I didn't check that they were on the proper posts.

[Dave_Darling]

That's a major red flag, then!

--DD

[vin man]

Did some testing tonight. I removed the headlight bulb from the socket on the driver side (this is the side I have the problem with).

Turned on the headlights and set to Low beam:
A- passenger side low beam works properly
B-Driver side voltage across white wire and ground is about 5.5V
C-Driver side voltage across yellow wire is about zero

Turned the high beams on:
D-passenger side high beam works properly
E-DS voltage across WHITE wire is now about 11.3 V
F-DS voltage across yellow wire is still about zero

According to my electrical drawing, the White wire is for HIGH beam and Yellow Wire is for low beam. So a little voltage is coming through the high beam side when I have the low beam on.

If I understand my drawing correctly (which is pretty scary as I couldn't read these things at all a month ago), it can't be the headlight switch or the high/low beam relay because they feed both lights at same time, not individually.

I think the next thing to check is to see if I am getting 12 volts on both sides of fuses 3 and 4 in the fuse block when the low beams are set to on.

[vin man]

Test above completed.

With LOW beams on, I have about 12 Volts on each side of Fuse 3, but 0 volts across fuse 4. I will need to remove the fuse block and check the connection because there is supposed to be a jumper between the fuse 3 and 4 on the feed side (according to my diagram which I seem to understand more each time I look at it). My concern is that, according to the diagram, the feed should be on fuse 4, and the jumper goes to fuse 3.

Will remove and inspect. Still looking for any other guidance.

[vin man]

Inspected and no breaks in the jumper. I cleaned the connections on both 3 and 4 on each side and everything works properly now!