Last fall, the drivers side headlight went out. it was miswired - I am not sure how it was working to begin with. Fixed the wiring, and everything worked great.

Saturday I washed my car.

Today, I decided to drive to work, even though rain was threatening, weather said I would be clear. But it was cloudy this morning, so I put the lights on. I got no beam from the drivers side light, again.

Also, I noticed that the charging system was right at 12 volts, where it is usually at 13. May be unrelated.

I know that the wiring at the light is correct. Any idea where to start trouble shooting?

Zach

I also see a voltage drop when my lights are on from about 13.5 to 12.5.
Did you check the fuse and fuse panel wiring? Since you fixed the headlight wiring I would work backwards from there to the fuse box and onto the switch.

I've had a problem with my old sealed beams before I removed them. The filament was broken off the stud, and turning the beam 90 degrees all the time, sometimes it would work and sometimes it wouldn't.

dont woory about the voltage drop zach, it isnt a true reading, the meter is on a circuit that always shows a huge drop whenever you turn somthing on. as far as your headlight... i am pretty sure i have a spare, i will bring it over after i pick lila up from school. will you be home around 4pm??


is mike over there too?

Mike may be over today. He was planning on being over as of last night.

I am using H4 bulbs, and have a spare at home - no worries there. But come over and wish Theo a happy birthday. he's 2 today!

My guess is that the other headlight is miswired and causing some weird issue. I'll have to look into it.

I'll be home ~ 4ish - in a conference right now, though - so its hard to say. maybe earlier, maybe later.

Zach

Did you check the relay?

Not yet. Noticed the light was out when I pulled into my office parking lot - and it was raining. Not a great time to start chasing wires. it will be something that I check tonight though.

ECHO echo(also headlight ground)

Start checking voltages right at the light.

If you can touch the terminals on the light with the socket on, check here for 12V.

If no voltage here, check each pin to ground to see that you have 12V and a good ground.

Work your way back to the light switch.

When I got home tonight I took a few minutes to troubleshoot int he drive way - but then the next squall came in and I got the car under cover with a quickness.

The low beam is out, and the high beam is really dim. Pass side works perfectly. I could go out and trouble shoot now, but I am supposed to be doing homework right now, and not posting on the World... And, its really cold out right now. I have a feeling that I am going to be fixing this in Mikes driveway next Friday.

Zach

Sounds like the brighter light is grounding itself through the dimmer one. I had that problem on my car at one point; I fixed it by providing a better ground for the bright light.

--DD

Dave, I considered this. I think it is probably the most likely possibility. After all, if I miswired one headlight - and it worked for a while - stands to reason that I could miswire two headlights, and have them work for a while.

Zach

Okay, so new puzzle.

I fixed the first problem. The headlight that was working was mis-wired (but working - weird...).

Put it back together, and I get light on both sides again! But, the low beam voltage is only 6 volts on the drivers side headlight (and is predictably dim). The high beam voltage is correct, and the headlight is bright. Passenger side voltage is correct on both high and low.

I tried a different headlight, and that was not the problem.

So. What would cause me to loose 1/2 voltage to the drivers side low beams?

Zach

How did you measure the voltage? Between which and what? If you measured the wires at the headlight, you could still have one light feeding back through the other. Or the ground could be messed up.

If not that, then look for lots of resistance somewhere. But I'd bet that the one light is still grounding through the other.

--DD

I measured voltage at the headlight terminals.

Where else should I check to make the problem more clear? How do I check resistance?

Zach

Well, Mike helped me chase the problem, and we found it was shorting inside the fuse panel. I am going to swap panels for Hershey, while mine get fixed.

Zach

So, this problem still exists.

I had been letting it slide and just driving my car during the day, but I got caught after dark last week and had a scary drive home

So far this is what I have done:
Replaced all the headlight relays - at the motors and on the fuse panel.
Replaced the high/low relay.
Soldered on new H4 sockets at the ends (I had no sockets, just spades)
replaced fog light switch
Tried running a new wire (test wire) that acted the same for low beams.

High beams work as expected (though they are aimed low as they are my only lights)
Low beams are only getting 6 volts at the bulb.
Driving Lights are not working at all. Need to puzzle that one out.

So I am back at my original question.
What causes a circuit to go from 12 volts to 6 volts?

Anyone got a headlight switch I can borrow to see if that solves the problem?

Zach

Possibilities:
bad headlight switch.
bad ground somewhere between the fuse box and the light.

Maybe I can help you out sometime

Didn't want to ask. I know you are swamped right now with the last tranny builds, fixing your own vehicles and getting stuff ready to move.

By the way, I found a snipped off red and white wire, and a snipped off yellow wire under the fuse box - I am guessing from the work done at hershey. any idea what they came from? I can't find any wire missing ends.

Zach

I remember nothing. I would have to start at it somewhat fresh. If you drove up here, you would be doing me a favor.

Goal here is to find where the other 6V is being dropped. Measure each bulb terminal to chassis ground. It could be a couple of things:

1) WRT chassis ground: one terminal is at 0V, the other at 6V: Most likely your switch, fuse, or wiring to each. Do the same voltage tests at the fuse (fuse to chassis). Fuse voltage on each side should be identical (no voltage across the fuse). Measure fuse voltages on the wire spade, not the fuse itself.

2) WRT chassis ground: one terminal is at 6V, the other at 12V: Ground issue to the bulb. Trace the ground wires and correct bad connection issue.

3) WRT chassis ground: one terminal is at 3V, the other at 9V: Combination of both ground and switch/fuse/wiring to each.

One test that I am going to do this evening, which should determin if the issue is upstream or downstream of the fuse box:

Unhook the upstream yellow wire that powers fuse 3&4 (low beam headlights) from the fuse panel. that should isolate the circuit from any of the relays or switches.

Put a test wire from battery + to input fuse 3.

The lights should turn on, as I am taking all the switches and relays out of the circuit. If I get full power, I know the issue is up stream of the fuse panel. If I get dim lights, I know the issue is at the fuse panel or down stream.

Any errors with this logic?

I should note that the lights are open right now with the motor relays removed so that they stay that way. Test would not work so well if I was lighting up the inside of the light housing.

Zach

Just finished my wire test.
Everything from the fuse panel downstream to the lights is golden. Full voltage.

So.

That leaves the headlight switch or a bare wire under the dash. I am going to go take the lower dashpad off so I can check it out. I'm guessing, though, that my switch is shot - and I don't have a spare one on hand right now.

Zach

I may have a spare. I know where I can get one, and I think you can use the bus one as the terminals are the same. There are options.

Disconnect NEG from Battery and pull out your switch. With the switch and the fuse panel safely not touching anything, find the TO and FROM wires for the lights, turn on the lights and measure voltages at these wires to chassis.

This should help isolate the switch as the culprit.

I'm back inside for the night, and I made progress.

I got my fogs/driving lights back up. Which means I will be able to see at night.

Once I pulled the lower dash pad out, and pulled the light switch down under the dash for examination, I started getting 10 volts at the low beams. Thats improvement. But they still take a second to build power - its not the instant on like the high beams have. Its almost like the low beams need a relay to switch in high volume current.

Now that I am sitting here typing it out, I did not look to see if the lights were instant on when I ran the test wire, but I believe that they were.

Anyway, I looked up at the under-dash wires and could not find a cut wire that might have been rubbing against the chassis. I am more and more convinced that it is the switch. Tomorrow I am going to button up the front end and get everything aimed. I am also going to run Spokes test and measure voltage at the switch. I was going to do that tonight, but I got tired. At the fuse box input, I have full voltage.

Zach

I wouldn't expect a rubbed wire or anything like that. If a wire were rubbing against anything you would have let the smoke out and it would have made a real mess and stink.

What I think you have is 30 year old oxidation on all the connectors. When you look at the connectors, there is a very very little bit of the connector actually touching the spade.

All around that small area of contact is exposed metal which oxidizes immediately and it builds over time. Just a little vibration and the vibration may be caused by heating and contraction, and the metal contact is now rubbing on an oxidized part of the lug and you get a bad connection and voltage drop.

Sometimes jiggling the wire (this is an official electrical secret) will improve the contact and your lights will get brighter. This is a hint as to your voltage loss.

You switch *may* be ok, just the spades and connectors are oxidized and need cleaned off with 400 to 1000 grit wet-or-dry sandpaper; dry of course. Contact cleaner sprayed after the sanding will remove the residue but it won't by itself, remove the oxidation. Your spades should look nice and shiny.

Also clean the edges of the connectors. I do this with a real little file. Sometimes I tighten the connectors by crimping (just slightly) the rolled parts of the connector.

Just this weekend I fixed the electric passenger window on my 911. The window would go down but not up unless the button was pressed time and time again, and even then it didn't go up fast. The culprit was; you guessed it; oxidized lugs. Cleaned the lugs with 400 grit W-or-D sandpaper and crimped the connectors and the window works like a charm. The oxidation on the connectors on my 911 is only 24 years old.

I'll clean them tonight and report back.
I am also going to do the wire mod on the headlight switch which will allow me to use my driving lights with the parking lights, so i don't need to raise the headlights to turn on the driving lights.

Those Pilots put out a lot more light then my headlights. I LOVE them.

Zach