Help Please! High beams blowing fuses.

[bikewhorder]

Can I still get a factory wiring harness?

[datzenmike]

Impossible. The headlamp relay simply provides a ground return for the high beams to turn on.

Here's how power flows...

Battery... fusible link... headlamp switch in ON position.... fuse box (two fuses for L&R high and low beams) to headlamps, all of them have power regardless.... head lamp relay selects either low, or high beams and provides a ground path to turn them on.

If you previously replaced the relay it is wired incorrectly.

Black goes to ground.

Red/White goes to all high beam filaments L&R sides (also to the high beam lamp in dash)
Red/Black goes to only the outer low beam filaments L&R sides.

1/ The relay grounds either Red/White OR Red/Black to turn them on.
2/ The relay default, or rest position when not powered is in the high beam position. Nothing is on as the headlamp switch is off.
3/ To power the relay and energize the coil inside, the parking lamp circuit is used. Without parking lamps, you cannot select low beams and your high beams stay ON. (see 2/ above)


Green/Blue is power to the headlamp relay coil from the parking lights.

Brown Red ...goes to ground by the dimmer switch on the steering column. It grounds the other side of the relay coil energizing it and turning it to the low beam position (see 2/ above) In the high beam position, the ground is removed and the relay defaults to the high beam position.

[bikewhorder]

Thanks for that thorough explanation! Its starting to come into focus for me. I've got a few irons in the fire right now so it might be a few days before I can get into this but I am going to figure this out soon. This problem existed before I changed out the headlight relay though so I'm not too suspicious of it, but I will look at it again. I can assure you though that my situation is not impossible, I melted down two fuses with no headlights connected just by hitting the high beam lever.

[Chickenman]

Time to start learning how to trace electrical shorts and wiring. Buy a 12 volt circuit checker and a decent Volt/Ohm meter if you don't already have them. A DVM with a Beep sensor for grounds can be very handy. Good Luck

Lots of good suggestions have already been posted. Time to methodically check them out one by one.

I would also suggest checking out your fusebox thoroughly. There is evidence of high heat and discoloring on the passenger side connector. Note the burn marks. You may find the electrical terminals are burnt and have high resistance. Probably because of the short. That will have to be corrected.

[okayfine]

In addition to the list of tools above, add a good wiring diagram. We didn't seem to actually determine the year of your car, but there's a full-color wiring diagram at The 510 Archives that will help you enormously.

[BrandonS]

Here's the Wiring Diagram from the Google Docs Archive with some highlights added. To see it bigger right click and open in another tab. I didn't color coat the highlighted lines to the wire color because I didn't think about it.

Yellow is energized when the headlight knob is pulled out all the way (it also includes the alternator line to the knob which is always energized)
Purple is energized with the low beams
Red is energized with the high beams
Blue is energized when the headlight knob is pulled out either to parking lights or to headlights; it represents the tail light's power

This is what I would say; if what you say about it only happening with the high beams is 100% true...
- At least this wiring diagram shows a 30A fuse for the headlight circuit; you mentioned you were blowing 20A (that's a 33% smaller capacity)
- It isn't anything yellow because then the fuse would pop with your low beams; same goes for the blue and purple
- It's not the ground side of the bulb's wiring. That wasn't in the circuit when you disconnected the bulbs and blew the fuse
- Focus on the red wiring and the items attached so I would inspect the following:
----Headlight connectors get disconnected quite a bit more than other connectors. Make sure the high beam pin isn't touching the ground pin in any manner. Also make sure the insulation on the wires goes into the back of the connector and doesn't stop before the back of the connector. This could allow the wires to make contact.
----The head light relay connector and passing light relay connector; check for the same as above; consequently you can disconnect one relay at a time and use the other relay to engage the high beams. As long as the connectors checked good this will check the relays individually.
----Disconnect your instrument cluster since the high beam indication bulb is ran off the high beam circuit. If the fuse stops blowing your instrument cluster has a short in it.
----Failing those things fixing it you will need to physically inspect the length of the wire. Pay special attention to the junctions where the line breaks into other segments and also look for abrasion where it passes through the firewall or any clamps.

[bikewhorder]

Thanks so much guys, I've been working like a dog trying to get my house and new workshop ready for winter and haven't allowed myself to get involved with this issue but I'm starting to see a light at the end of this tunnel and I should be working on this in relatively cozy shop in a few weeks. I'll let you when as soon as I track down this problem. -Chris

[Chickenman]

The 1968 wiring diagram won't help Chris much as it appears his car is a 1970.