Street Rat

I recently had a problem on my 81 with my headlights turning off unexpectedly. I have installed halogen headlights and I believe this caused the circuit breaker in my headlight switch to trip. I decided to put relays into the headlight circuit to take the load off of the headlight switch and increase voltage to the headlights.

These are the basic components that I'm using. Just double what you see here. I ran a separate power wires and circuit breakers for the low beam and high beam circuits. 12 gauge fuse holders, SPDT relays, and resettable circuit breakers (15 amp and 20 amp), lengths of 12 gauge red, 14 gauge tan, and green wire.
You can use a SPST relay as I didn't use one of the output circuits (87a) of the relays.



I simply spliced into the tan and LIGHT green headlight supply wires exiting the dimmer switch. These wires may be different colors on your car. Be sure and check a wiring diagram for your specific year model. DO NOT splice into the DARK green wire as this is the horn circuit. Access to these wires were located inside of the left fender. I ran my 12 volt supply wires from the alternator to the relays (not shown). The ground was attached to the engine (not shown).



Here are the relays installed next to the wiper motor on the firewall. I finished everything off by covering all the wires in black convoluted tubing (not shown).



Here is the schematic that I used to wire my system. Although it only shows two headlights the relay wiring is the same.



The mod was a success as the lights are brighter and I will have no problem with them tripping the headlight switch circuit breaker ever again.

moonsteel

This is on my list of todos this spring, although I plan to use 3 relays so all four lights are on with the high beams. Once I'm done installing it, I'll add my pics here so people can find both options when they search

Street Rat

All four of my headlights come on when the high beams are on.

moonsteel

1974

MIKE80

Can the factory headlight wire harness that you spliced into handle the voltage increase to the headlights or did you replace the factory wires with larger gauge wires?

Learning_Curve

He has the factory wiring doing nothing more than controlling the relays. So the circuits that once powered the headlights are now flowing a fraction of an amp.

And the new lights would raise the amperage requirements, not voltage.

Kid Vette

Definitely a worthwhile mod. Best if you run a separate 12 gage wire to each headlight though.

Street Rat

I didn't run new wires out to the headlights. If I have problems with the mod I'll change the forward wiring harness to larger gauge wire as Kid Vette did.

Kid Vette

This has been posted many times before but I think its been a while so I'll post it again. This is a good read.

Relays: WHY AND HOW TO UPGRADE YOUR HEADLAMP CIRCUIT

Street Rat

GREAT article Kid Vette. Thanks for posting it.

alconk

Do you have any photos of your positive wires coming off your alternator? That would be helpful to me and where exactly did you ground it on your starter?

Thanks!

Street Rat

I'll go take a few pictures and post them for you.

Street Rat

alconk I sent you a pm containing photos.

alconk

Excellent! Thank you very much.

hugie82

Stock 81 lights im pretty sure are halogen. If your light switch is going bad, I would replace it! Just to be safe. Nice wiring job! A few relays couldn't hurt

MSGT-R

Thanks. Good thing to know when I'm doing major stuff forward of the firewall.

Hop's 78

This is my winter project. Just put the H4 (?) halogens in mine a few weeks ago and with high beams on the lights would blink off and on. My solution for the short term was to unplug the 2 center lamps so I still had the low/high outer lamps and they have been fine that way.

doorgunner

The set-up looks good.

IF you do have any problems later on---you might want to buy better sealed relays---the relays off-the-rack don't last long in the engine compartment!

alconk

Can anyone reconmend a good relay to buy and where at.

Street Rat

I used some made by Directed. They make car alarms. You can get them online at most car stereo sites or Amazon. I always have a couple spares in my glove box just in case.