Headlight gremlins Options

[john77]

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.

[Spoke]

Are they off and turning themselves on?

Or on and turning off?

[john77]

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.

[taylspin46]

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

[bdstone914]

@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?

[john77]

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

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.

[SirAndy]

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

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.

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[john77]

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

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.

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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?

[john77]

@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 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.

[Spoke]

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.

[Costa05]

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

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.

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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?

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.

[john77]

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.

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.

[john77]

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

[Mikey914]

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.

[SirAndy]

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

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.
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[lierofox]

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

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.

[john77]

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

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?

[FlacaProductions]

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.

[dr914@autoatlanta.com]

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

[john77]

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.

Great thread. Thanks for sharing.