H4 dim headlights on low? Not the TS switch
 

Car is a 86 930 with H4's.
One day the low beams just went dim, but the high beams were fine as well as the flash function.
Turn Signal stalk is new, even temporarily swapped in a good used one...no change. Fuses are all new. Checked and cleaned the ground by the battery. Opened up the H4 buckets and all wires are proper and even swapped out the bulbs.....no joy.
Voltmeter time.....I have 6v going to the low beams and 12v to the high beams at the headlights themselves. HOW is this happenening? I have 12v at the low beam and high beam fuse blocks when that particular beam is selected.
Any ideas? Can the headlight switch do this? It dims the dash lights well and all the connections are good.
I'm loosing my mind!!!!!
Thanks,
Andrew
86 930
Autronic EFI

How did you conduct your voltmeter tests? I ask because it may be that the dimmer relay that switches from high to low beam may be faulty and the fault only shows up under certain test circumstances. Since you have 12v at the fuse block but only 6v at the headlight under the test you conducted, it appears the fault is in the wiring/grounds between the two points. However, since the problem developed suddenly and in both lights, that points to a common element for both that may be a problem source.

Do the lows ever come on full power--like when you first turn on the headlight switch on the dash?

One more thing, where did you measure the voltage for the low beams at the fuse block? Was it on the single yellow wire side or the separate two yellow wire side? If you measured at the single wire side and got 12v, as you should, but didn't measure on the two separate wire side, you may have missed the fault. If you get only 6v at each separate (load) wire, then the fault may be in the "jumper" in the fuse block that splits the 12v single power wire into the two 12v wires to the lights.

When I intially turn on the low beams they appear bright (not normal bright) and then fade into the dull glow.
As far as the voltmeter goes I checked both the upper pole and lower pole and received the sam readings. I also checked for continuity between the individual fuse blocks and that was good...so the metal strip behind them is intact.
Is the fade from brighter to lower an indication the headlight switch is bad?
Also, can you give me the reader's digest version on how the electricity actually runs from the battery to the headlights?
Thanks!!

had a similar issue with my H5s. Mine was a dirty contact in the headlight connector. I ended up replacing the contacts since they are so small I couldn't clean them. you might make sure all your contacts are clean.

I have three connections to the H4 bulbs, all are super clean. The Low beam wire has only 6V...

Simple version: Current flows from battery to ignition switch, to headlight switch/stalk switch, to dimmer relay, to fuse block (very, very simplified but enough to let you know that the power to the fuse block has passed through switches and relays.)

Have you measured the voltage at the fuse block during the conditions you describe--starting out bright and fading? If you are getting 12v at the block on both sides of the fuses when the lights are dim, then the problem has to be further downstream and not in the switches.

Question: Do you have an aftermarket set of headlight realys added to the car? Typically they would be wired in before the fuse block and, if faulty, you'd find a drop in voltage at the fuses. However, if they were wired after the fuse block, the fault could be there.

From the information you've posted, I'm a bit puzzled too. If the voltage at the block is constant, the drop has to be somewhere along the path to the headlights.

edit: Have you traced the path of the yellow wires from the headlights back to the fuses? Yes, they are in a loom, but possibly someone has tapped into the loom or rewired the low beams. Because they both failed together, try to find the common link between the two circuits between the fuse block and the lights. Not familiar with the 86, but there may be a multi pin plug connector somewhere along the wire loom. If so, clean the pins and reinsert to see if that is the problem. Also, test voltage at the connector, if present.

NO relays....yet.
Off to the garage for a quick reverify on things.
Back in 10

UPDATE
Very wierd. Here's the latest volt readings
Headlights on low:
12v on both low beam fuses, upper and lower poles....DIM HEADLIGHTS. Checked the high beam fuses while still on low beam (for the heck of it) and these show 6v.
Headlights on high:
Beam is bright and I have 12 v on ALL the four fuses...low and high beam.
What the heck is going on?

O.K., now I am guessing but I hope wiring experts are followin this thread and will help out.

This suggests to me a problem with the grounds for the headlights which causes a poor current flow (amps) and a feedback into the highbeam circuit. If I recall correctly, you should not have any voltage present on the high beams when the lows are on so the voltage you are reading is actually a draw from the low beams--maybe at the headlight itself.

Try this test. Unplug the connectors from the headlights (both). Turn on the headlights and measure the voltage at the connectors for the low beams. Then, measure the voltage at the fuse block for lows. Then measure the voltage at the fuse block for the highs.

If my understanding is correct that the highs should not be powered and there is no voltage shown on the test, then the 6v you found is being fedback from the connection at the headlight--possible ground fault.

Just a theory. Post your results if possible. Still could be problems with the headlight switch, dimmer relay, or connectors along the loom from the ignition to the fuse block.

Been thinking a bit about this and, as I said, I'm no wiring expert, but here are my thoughts.
If you reconnect your lights and remove just the fuse for the high beams, what happens? Are the lows bright as they should be? Do you get a voltage reading on the power terminal of the high beam?
The place where both the high and low beam circuits are common is at the dimmer relay. Possibly the relay is faulty or poorly grounded and this is where the current bleed is happening. Again, I hope someone who has more experience can confirm these ideas, but at least they are relatively easy to check out and not expensive.

Maybe I just need new bulbs. Reason why:

I disconnected the bulbs and used jumpers directly to the bulb connectors themselves. High beam is good, low beam is dim.
Can H4 bulbs do this? I thought they either worked or didn't.

Yes, it is possible and it's a simple test. I've had bad bulbs that began to fail by going dim before fully failing. This could account for a voltage feedback too. If it were me, I'd try two new bulbs. You've got nothing to lose and at the worst, you still will have to find the problem but you have two spare bulbs.
Let us know your results.

Last question before I'm off the to parts store.
What wattage? Bulbs right now are 90/100W.....

UPDATE:
Problem solved!!!
http://forums.pelicanparts.com/porsche-911-technical-forum/478483-update-h4-dim-headlights-low-not-ts-switch.html

You are welcome ;-)

Glad it's solved. With so many possibilities, it's nice to know the simplest and cheapest solution was the one.

Did that solve it?
Mine seem a little dim at idle. They get brighter if I give it some gas.
The high beams work great.

I think my brown wires are on the right if you look at the connections.
Just reversing them makes that much of a difference.

Hmmmmmm, maybe I'll go out there and try it.
Were you having the same problem?
Dim at idle, brighter if you raise the RPMs.

No increase in brightness with increased rpm....make sure you check you alternator output and grounds.
I had a steady very dim light on low beam. Turned out I had inadvertently switched the ground and high beam leads. Imagine the bulb pointing away from you, lead 1,2,3 in clockwise position from left to right:

lead 1-ground
lead 2-low beam
lead 3-high beam

Here's the link to the diagram from another lister

http://forums.pelicanparts.com/porsche-911-technical-forum/80335-dim-low-beams.html?highlight=dim+headlights

Just scroll down, you'll see it.
My headlights are now nice and bright and the relay kit is going on soon.
Drew
86 930
Autronic EFI