Electrical (headlight relay) questions

[ARAMP1]

I installed relays in my headlight circuits (high and low beams) in my 68 GTO about a year ago. I also did all new wiring from the relays forward. It made a heck of a difference. It had been working fine for about a year now.

Anyway, one of the lights burnt out and another took a rock directly to the glass. It still worked, but there was a chunk of glass missing. So, I decided to replace all four headlights. I had them in for a couple weeks and the other night, I was at a stop light next to a buddy, and we were fooling around. I did a burn out (headlights on) and they burnt out. I switched them over to the brights just to get home and they immediately burnt out.

Upon inspection, all wiring is fine, just must have been a voltage spike or something. I still have an old externally regulated alternator. Maybe that has something to do with it. I had a 30 amp fuse that I switched out for a 20. Hopefully, if it happens again, the fuse will take the hit and not all four headlights.

Anyone have any suggestions as what to check or change?

 

[Jessie James]

I had a car that did that. It was a loose connection to the battery from the alternator. Check for a tight connection. If you "remove" the battery from the system, the alternator will send a huge spike through the system and blow a lot of lights.

In my case the battery terminal split in half so it look like it was attached but really wasn't. I put a new one on. Maybe you have a loose terminal, loose wire, or something like that.

 

[Fordum]

Yep, like Jessie said, you may have lost the connection from the alt to the battery. Or, you may have lost the ground reference to the regulator.
Lots of times they are grounded to whatever they are mounted on, and if they come loose, they don't know what voltage they are reading and just let the alt crank it out.

You need to put a voltmeter across the battery terminals and then from the alt terminal to ground ASAP.

An uncontrolled alternator can burn up lots of stuff real quick.

 

[trustyrusty]

I would suggest that you also check your voltage regulator.
I doubt there was a short of any kind, as that would most likely blown the fuse, but I may be wrong as I don't know if the relay(s) would hide a short from the fuse. Is the fuse the one in the factory fuse box or is it a fuse between the relay(s) and the battery/alternator? You do have a fuse there i hope.

 

[ARAMP1]

I would suggest that you also check your voltage regulator.
I doubt there was a short of any kind, as that would most likely blown the fuse, but I may be wrong as I don't know if the relay(s) would hide a short from the fuse. Is the fuse the one in the factory fuse box or is it a fuse between the relay(s) and the battery/alternator? You do have a fuse there i hope.

Yes, I'm talking about the fuse that I put in between the relay and the alternator. Both that one and the regular headlight fuse were good (along with the relays themselves). I'm wondering why I didn't blow any other lights. Just the headlights.

 

[Fordum]

Yes, I'm talking about the fuse that I put in between the relay and the alternator. Both that one and the regular headlight fuse were good (along with the relays themselves). I'm wondering why I didn't blow any other lights. Just the headlights.

If it is hooked up exactly like you show, then the headlights would get more of the trouble from the alternator than the rest of the lights.

The battery would absorb some of the overvoltage, and the wire from the alt to the battery would help limit what the rest of the car got.

In other words, the battery would respond to the higher voltage by increasing the current going into it. The wire between the battery and the alt would have some resistance, as would the wire coming out of the battery going to the rest of the car.

Due to the high current going into the battery, that resistance would cause a voltage drop across that wire.
Your headlights, if wired the way you show, would not see any of that voltage drop, since they were not in that circuit.
They were getting their power direct from the alt and would get full voltage.