71 GT Head Lights

[Paul]

I need to know how /what makes the head light actually turn on. I know it sounds like a grade school question, but I'm a lifetime Manta guy, never owned a GT much less one that didn't have butchered wiring. When I got the car, it had a switch hanging by some speaker wire under the dash.

Someone please describe the correct process including rolling the headlights over. I will say this, the micro switches for the buckets are working correctly.

I was given the impression that some switch on the dash needed to be replaced. The only factory installed toggle switch on the dash operates the running/parking lights and one operates the dash lights. What turns the head lights?

Thanks

[greensmurf20]

other more knowlegable people could get you a real specific answer. the wiring was changed between the 70 and 71 model year. in general, when you roll the headlights over, 1 microswitch (i believe pax side) will operate the white light in the dash telling you if the headlights are in a locked position, or if they are not locked. the drivers side will feed power to the headlight relay(s) which inturn feeds power to the headlights themselves. very general i know but i hope it can help you. as far as i know, the rocker switch will only turn on the running lights and dash lights, the headlights will only come on if the key is on, and headlights are in the up locked position.

i did have a 70GT, that the rocker switched turned on headlights, running lights, and dash lights, whether or not headlights were up or down but the wiring was hacked in that by the previous owner and i wont use that as a legitimate example, because i also had a 70GT as a short project car that worked identical to a 71 or newer car, with great wiring.

[john4856]

Maybe this post should go in the humor forum but i had to say that i spent about 25 min. looking for my headlight switch. Had to get my service manual out to find out how they worked. Just could not understand why it had a switch for the parking lights but not for the headlights!! ( my first gt ) Boy have i been educated since then. Had to rewire the headlights, rebuild the calipers, replace brake lines, replace a smokin ignition switch, replace gas tank vents, fix temp. and fuel guage. More to come im sure.

[Paul]

So, I roll the head lights over and the white light turns off and the headlights come on? Jared is that what you are saying?

I really do appreciate everyones help.

[greensmurf20]

yep, white light should be off when the headlights are closed or open, only one while they're rolling over. but yep, white light off, headlights on when key is on and you roll the lights over.

[kwilford]

Come on Keith, moving it is fine, but at least provide an answer. This is something ANY GT owner can answer.

I will assume that this comment was made in good humour. If I find otherwise, bad things happen to offending members' posts

OK, I was heading out to dinner with friends, and "she who must be obeyed" was kinda' urging me to get OFF the computer. Besides, I don't like to hog the spotlight. We need to let the other members get some time in as well...And besides, why didn't YOU answer it, if you own a GT ?

OK, here's the story. IF (and that's a BIG if!) the wiring hasn't been butchered by the PO (Previous Owner, also called other names, none of which are repeatable on this PG site), the GT headlights work something like this:

1) Power for the headlights comes from the main fuse box, without benefit of a fuse or circuit breaker, just the main fusible link(!!), to a silver relay under the dash near the fuse box called "headlight relay" (we'll call it the "HR" for simplicity, and because I am an engineer and us engineers can't spell worth a damn, type poorly, love acronyms and are kinda' lazy).

2) A relay is a switch, which closes (allows power to go through) when a second source of power is applied. In simple terms, there is a little electric solenoid inside (just a electromagnet and a set of contacts) that closes when power is applied to it in this case. The HR is only energized (a fancy way of saying the contacts are closed by the solenoid) when the ignition is on. So when the engine gets shut down, the headlights go off.

3) The power to energize the HR comes from a single microswitch behind the driver's side headlight rotator mechanism. When the headlights are rotated out of the "closed" position, the microswitch closes, sends power to to the HR, which in turn sends power BACK to the headlights, and they make the world a brighter place. Seems like power goes back and forth for no good reason, but the Opel engineers thought it was cool.

4) In case the headlights weren't fully opened (or closed), the engineers decided to give you a warning. They put another microswitch behind each rotator mechanism (so two in total behind the driver's side, including the HR switch, and one behind the passenger's side) that causes the white dash light to light up if the buckets are "in between". Either re-close and re-open the headlights, do some exercises to strengthen your arm, or repair the damaged headlight mechanisms.

5) Before the power goes to the headlights, it goes through another relay, right beside the HR, that is the Dimmer Relay (yep, DR for short). This relay is "tripped" (as in toggled) back and forth between "Low Beam" and "High Beam" by the turn signal stalk. Early ('68 to '70) models had a push button on the end of the turn signal stalk, later ('71 to '73) used a more conventional back and forth motion of the stalk. Pushing the button or pulling the stalk grounds out the solenoid in the DR, which energizes it, tripping a set of contacts to either allow the power to go to the high beam or low beam wire.

6) This is my favourite part. The headlight wiring! The wires that leave the DR are properly insulated. About the middle of the engine compartment, they split into two more wires (one for the right side, the other for the left; well, four more, since there are high and low beam wires to each headlight, plus a ground to each light which comes into the harness at the radiator support). But Opel figured that since GT headlights rotate, they had better use a different insulation from that point. So the wires from the split are insulated with rubber, rather than plastic. And they ARE more flexible, for about ten years. Then the insulation spontaneously crumbles, and allows the low beam and high beam and ground wires to touch each other. Magic! Fireworks! SMOKE! The resultant short circuit (what the electrical engineers call a power flow from a battery directly to ground without a resistor (light bulb or heating element) or inductor (electric motor) to convert the electricity to useful work) causes the fusible link to melt (if you are lucky!).The CO (Current Owner) attempts to "repair" the wiring, because he knows WAY more about wiring than the PO, and leaves the FO (Future Owners) with a mess of unintelligible wiring. Probably the main reason that GT's get abandoned (aside from funky Solex carbs).

For more information, open a FSM (Factory Service Manual) and trace the wiring diagrams. And read the other threads in this Forum (which was REALLY why I moved your thread here).

HTH.

[Paul]

Jared,
Thanks thats the answer I was looking for. I got some mis-guided info from the person who 3rd partied the car sale to me.

Keith,
It was 50% frustration and 50% good humor. Remember, I've NEVER owned or worked on a GT before. I was bitchin' 'cause you had time to move the thread but not time to answer the question. At the time I had the dash open and just needed the answer that Jared provided. No point in replacing the Parking light switch if it didn't turn the head lights.

Keith,
I DO want to thank you for your detailed explanation above. Now I can begin the trouble shooting process.

Thanks Everyone