Mike wrote:
> Have you done it, and which wires did you
> use for high and low beam control going into
> the relay?
Well, there are several methods, depending on just what you're trying to accomplish. Like most things in life, the better methods are more work.
Let's start with a quick explanation of how the headlights are wired and go from there.
Power goes from the fuseblock directly to the common terminal on the headlights, one wire and fuse for each light. The low beam terminal from both lights are connected together and run to the dimmer switch. Same for the high beam. The common terminal of the dimmer switch goes to the headlight switch. The headlight switch grounds the lead to the dimmer switch when the headlights are turned on. In later cars, '73 for sure and some '72's, there is a passing relay connected to the high beam circuit which grounds the high beam connection between the lights and the dimmer switch. This was (I think) an attempt to keep the switch from melting.
There's a couple of problems with the stock setup and the approach to take when adding relays depends on which of the problems you're trying to cure.
Problem 1: The high current through the headlight and dimmer switch cooks the switches.
Problem 2: When using halogen conversion lights, the case of the light is GROUNDED. This shorts out the power from the fuseblock to the common terminal of the lamp. It usually doesn't short it out very well, not necessarily enough to blow the fuse, but it can eventualy melt the fuseblock. The lights also don't work very well because some of the current doesn't go through the light.
You can solve problem 1 as follows You need two relays (one for high beam, one for low). Each relay handles both lights so get at least 20 amp relays. Get normally open, or Form A relays.
Connect as follows:
Common load contact of each relay to ground. There's lots of current here so use a big fat wire and connect it to the big ground wire in the engine harness.
Cut the high beam wire between the lights and the dimmer switch where it runs by the relays. Connect the part coming from the lights to the Normally Open load contact of the high beam relay.
Connect the part coming from the dimmer switch to the negative relay coil terminal. Some relays don't care which is negative, some do. Check yours to be sure.
Connect a 12 volt source to the positive coil terminal. You have your choice here. You can use either headlight power lead, or run another fused (2 amp) lead to the battery or whatever. The problem with using a headlight power lead is that you lose BOTH your headlights if that fuse blows. You can combine the headlight power lines together with a pair of diodes if you like (that's what I used to do). Write me for part numbers and wiring procedure if you want to do that.
Do the same thing for the low beam relay.
To solve problems 1 and 2:
Now you need FOUR relays (or you have to rewire the fuseblock or run a common fuse for both headlights. On the other hand, 10 or 15 amp relays work fine 'cause each is only carrying current for one filament. Or you can use two pole relays -- then you only need two. I'll describe it as four relays because it's simpler to explain, but the other ways are probably better.
First, the coil wiring is exactly the same as for Problem 1 above. Except that you have two relays for each of high and low beam. Just connect the coils in parallel for each beam.
Cut the power wire from the fuseblock to the common terminal of the right headlight near the relays Connect the part coming from the fuse block to the common load terminal of the two right headlight relays.
Ground the part of the wire coming from the headlight. Connect it to the big black ground wire in the engine harness.
Do the same for the left headlight power wire.
Run new wires from:
Left Headlight high beam terminal to Left High Beam Relay Normally Open load contact.
Left Headlight low beam terminal to Left Low Beam Relay Normally Open load contact.
Right Headlight high beam terminal to Right High Beam Relay Normally Open load contact.
Right Headlight low beam terminal to Right Low Beam Relay Normally Open load contact.
You can, if you like, use the existing wires for one headlight or the other but you have to run new wires to the other light.
I could send a wiring diagram, either by fax, or possibly scanned in if you'd like.
I didn't mention wire colors, because I'm not sure that they're the same for all cars, but if you tell me what your wire colors are, I'll match 'em up with my wiring diagrams and tell you what is what if you like.
Good luck,
Pat
Remove the passing relay if it exists. Just unplugging it is fine.