My headlights have decided to randomly turn themselves on and off as I drive, which is a lot of fun at night on the I405 as drivers think some obnoxious d*ck is flashing them.

I cleaned up the grounds and all the ground wire connectors by both headlights but it’s still happening.

Could this be relay connected, or are they more a once dead completely dead kind of deal?

I thought i’d ask before I drop $20 on a new one.

For the record, I have those sealed GE led headlights, and it’s happening simultaneously to both, so I know it’s not the bulbs.

Are they off and turning themselves on?

Or on and turning off?

They’re on and turning off.

And then on.

And then... you get it.

There doesn’t seem to be much rhyme or reason though. It’s not happening every time I hit a bump or anything - it’s happening sitting still in traffic too.

Sounds like headlight switch contacts. Pull switch and see if you’re losing power.
Does it do it with high beams also?

@john77

My bet is the switch.
The lights have separate relays and fuses.
Is your car a 73?

Will they undo that if you wiggle the switch shaft?

Thanks, I’ll take a look at that.

I’m not sure if it does it with the high beams too, it’s one of those gremlins that’s hard to replicate - every time I turn the lights off and back on they initially work again... until I start driving.

No and neither. There's no relay for the headlight power, the relays next to the headlights are for the motors that move them up/down.

I know the relays next the the headlights are for the motors. I meant the how/low beam relay under the dash. If it was faulty couldn’t it still stop the power to the headlights?

Thanks Bruce. Yep, it is a 73.

So that's two votes for possibly the switch. Thanks guys, I'll take a look at it. If it is, I think I may have a spare hiding somewhere in my closet of spare parts.

Here's the circuit for a '74 914. Likely the '73 is similar if not identical. If both headlights are turning on/off then as others said is likely the switch.

Coincidentally I was just looking at the wiring diagram for the high/low beam relay under dash on my 73. Yes that relay is fed off the dash switch. Its a two position relay. The "at rest" position feeds low beams. When the relay is activated it jumps over to the high beam side. Both sides of the relay then run through your fuse panel. Fuses 1 through 4. Then goes to headlights. Lt Rt low beams....Lt Rt high beams positive wires. The relay is cheap if you want to replace it. Can be bench tested but replicating could be tough. Worth cleaning all five spade connectors first and take it for another drive. Mine were pretty corroded.

Oh, this is great, thanks man.

My fog lights aren’t working either, but that’s another story...

I fitted the Jwest harness a couple of years back so I could use my fogs as driving lights.

About 12 months later I got a pair of the GE nighthawk headlights and every time I switched on my fogs the headlight motors would start doing weird shit opening and closing even though my headlights weren’t switched on.

I ended up disconnecting the jwest harness but I’d still like to reroute fogs so I can turn them on without having to turn on my headlights.

@spoke Am I reading that diagram right, the fogs only come on when the high beams are on?

If it's the lights (both going up and down), it has to be the switch. Unless both relays have failed in the same manner at the same time (possible but remote).

If the switch is coming apart internally it will move around and could do exactly what you are describing. You may also have other issues, but I'd put money on the switch.

No, the fog lights go out when the high beams come on.

It's illegal to run fog lights and high beams at the same time. Well, at least in Europe it is.

It's one of those wonky to understand, but very useful circuits.

The ground side of the fog lamp relay is connected to the positive side of the high beam circuit. When the high beams are off, the high beam circuit is dead, so the relay is able to find ground by going through the high beam filament (the current going through the relay coil is so low because of the coil's high resistance (not even 1 amp) that it's not nearly enough to make the high beam filament glow.)

When the high beams are turned on, the supply side of the high beam circuit suddenly becomes 12 volts. Since the fog light relay coil has 12v on one side, and 12v on the other side, the difference between 12v and 12v is... 0 volts, so the relay turns off, and kills the fog lights!

Because bulb filaments work differently from LEDs, this circuit can break spectacularly when you replace the headlights with LEDs.

Wow, I didn’t know this... and it just gave me a headache trying to understand it.

So my best bet if I want to run fogs with the LED headlines is to completely separate the two circuits and run the fog switch directly to the fog relay?

There's a ton of info here on the LED headlight/fog light "issue" but take a look at this thread (after you get your switch sorted) and it'll get you going:
https://members.rennlist.com/demick/fogrewire.html

Also search "EP26" from @Spoke - that'll point you down the correct road as well.

probably the headlight switch or the high low beam relay. As it is cheap, I would replace the relay first.

Great thread. Thanks for sharing.

You just have to pull the fog relay's ground wire off the high beam terminal, and move it over to a dedicated ground lug, then it'll always be grounded and the high beams won't cancel it.

Edit: Here's a little interactive/animated diagram I made demonstrating the circuit, you can click on the switch to turn it on and off, the wire colors show where the voltage is (green is 12v, gray is ground) and the yellow dots show the current flow.

http://tinyurl.com/tj74k43

Hijacking the thread since my issue is light related.

My light were working perfectly until about 4 nights ago.
The drivers side headlight does not go up when I turn on the lights. The light bulb is on but I have to turn the knob on the back of the motor to manually raise the light up into position. I will check the relay. Is there any other typical cause of this kind of issue I should check?

Sounds like the relay if the light's coming on. I went through exactly the same thing before I got around to putting in a new relay... and then these new gremlins appeared.

Just unscrew the plastic covers on the side of the motors, swap the relays over and turn your lights on - if the opposite motor to the one not opening now doesn't work, you'll know within about 5 minutes if it's the relay or something else.

That makes sense.

Moving the fog relay ground wire, the power to the fogs is still dependent on the headlights being switched on?

If I wanted to use them as independent driving lights I'll need to find a new power source to trigger the fog relay directly from the fog light switch, right?

Yep! I forget which one but I think I pull power for my switch from either Fuse 8 or Fuse 9 on the under dash panel, so it'll still turn off with the key.

I'd bet relay try to wiggle it around may just be a bad contact in the socket. But typically that would be a relay.







Anyone want to put me down for $5 on the switch for this thread

I took the car out last night. Still no conclusive answer.

Warming up on my driveway, lights on, they work fine. 10 minutes sitting there, not a glitch.

I drove 20 feet down the street and they cut out. I tried waggling the switch, nothing.

I turn them off and back on and the lights either come straight back on (and then die) or they flip up, nothing for about 10 seconds, then they come back on, then they die.

Is waggling the switch supposed to have some effect if it’s the switch?

Looking over the wiring diagram there's a few possible candidates for a single-point-of-failure for the headlights.

From the ignition switch: Terminal X feeds power to a separate wire that leads over to...
The headlight switch: When pulled to position 2, power is supplied from input terminal 15 to output terminal 56. From there it heads over to...
The Dimmer Relay: Power comes in on terminal 56, and outputs to either the low beam terminal (56a) or the high beam terminal (F) and both lead over to...
The fuse panel: The low beam wire feeds to fuse terminal 4, which is always jumpered to fuse terminal 3, the high beam wire feeds to fuse terminal 2, which is always jumpered to fuse terminal 1.

At this point all 4 functions have split off to separate wires (low left, low right, high left, high right.)

If your low beams die, but you hit your dimmer lever and get high beams, I would inspect the wire between Fuse 4 and the dimmer relay. If those look good and solid I would condemn the dimmer relay.

If your low beams die, and your dimmer lever doesn't give you high beams, I would inspect between the dimmer relay terminal 56 and the headlight switch terminal 56 (if equipped, this terminal also supplies power to your fog light switch, terminal 15.)

Before condemning the headlight switch though, also inspect the power going to input terminal 15 on the headlight switch. If power is intermittent there, that means your ignition switch is suspect, try wiggling your key in the ignition and twisting it slightly, see if any sort of motion will cause your headlights to drop out without also killing the engine.

If your ignition switch seems fine, and no amount of wiggling it seems to set things right, you can try servicing the headlight switch. One of the failure points of the headlight switch is that the sliding contacts get worn/pitted, you can try disassembling it and inspecting the contacts and the springs that hold the contacts down. If excessively worn, I believe that 2 of the contacts are actually identical, and you can swap them around and reassemble the switch. (Not sure if this is the case for a '73 switch, it was true in my '75.)

From personal experience on my own 914, I've had problems with all 3! Replaced the ignition switch, serviced the headlight switch, and replaced the dimmer relay.

I went out to check the relays. Before I touched anything I pulled the switch to turn on the headlights and got the same behavior, the passenger highlight popped up and both bulbs turned on.
I pushed in the switch to turn off the headlights and the passenger light went down half way and stopped and both bulbs turned off.

I swapped the relays and pulled the switch. Both bulbs turned on but the drivers side stayed down and the passenger side stayed half down.

It looks like the relays are not the problem. Now I have to find out what is the real problem.

Wiggling the switch may not cause the issue to happen. Likely it's vibration introduced with the movement of the vehicle. Pounding on the dash may get the issue to occur but not guaranteed.

If it is the switch then you have to bypass the switch to test or just replace the switch. I'm not a fan of just replacing something w/o testing first. It could even be the connections to the switch or to the hi/lo beam relay.

Whatever you do to test or replace the switch, remove the negative battery terminal before touching any electrical components. There is no fuse between the headlight switch and the battery. Accidentally shorting something could result in burned wires.

This thread gave me a headache

I have a drivers side headlight that sometimes does not pop up but the light is on. I found that if I do a quick push on the front of the headlight it will bobb down then up, and away I go. Almost got the finger caught one time though

Oh yeah, been there done that and learned my lesson. I fried about 6 inches of the wire into the fog relay by accidentally touching two of the socket terminals when the relay was out. What a royal pita that was splicing new wires into the harness and making sure I found every last piece that was burnt.