Headlight Relay Install. What do you think??

November 09, 2004, 08:26:33 PM

I have found this article recently in a Hot Rod magazine about installing a relay to brighten up the headlights. Here for the link to the article:

A Quick and Easy Headlight Upgrade

I was playing around with this on our Cougar. I know the article shows the older style headlights (prior to 87 on the cougars & tbirds) on a chevy.I know the newer style headlights are supposed to be brighter. I have gotten a reading of 14.44v at the battery & 12.56v at the headlight (low beam). After rigging up a rekay set up, I got 14.38v at the battery & 14.10v at the headlight (low beam). By doing this, I picked up almost 2v at the headlight. Would this create any problems to our cars such as the headlight overheating, wires getting hot, etc...?

Re: Headlight Relay Install. What do you think??

Reply #1 – November 09, 2004, 09:48:54 PM

Shouldn't cause any problems. It also lightens the load on the headlight switch. Very costly to replace that switch. If you go with higher wattage bulbs you should do it anyway. I'd say go for it.

Re: Headlight Relay Install. What do you think??

Reply #2 – November 09, 2004, 10:28:55 PM

Actually the switch is somewhere around $20 (I had to replace it in my '87 after melting it with 80/100 bulbs).

The relay is a very good idea, and when done right it is also safer. The shorter distance you're carrying high current, the better. I have 12 gauge wire running from my battery to a fog lamp relay mounted on the inner fender and then 14 gauge down to the fog lamps themselves. I used a Bosh 0332-019-150 relay (two "87" terminals, no "87a"). This allowed me to run a wire from each "87" terminal to an individual fog light. Each section of 14 gauge wire is only carrying about 6 amps qith the 55-watt H3 bulbs.

Using the relay allowed me to run 16-gauge wire into the passenger compartment and to the switch. The switch gets its power from an ignition feed on the fuse panel (prevents me from leaving 'em on), and as the switch only controls the relay there is only about 50mA passing through the switch.

I'm a firm believer in relays. I don't like to see switches carrying any current. I installed a 75-amp Bosch relay at the IGN output on the remote starter (connected to the grey/yel wire at the ign switch) because too much current would've flowed through it (the heater fan, inst cluster, radio, and more). I eventually plan on changing the relay installation so that the ign switch doesn't carry all of this current either. I also installed a relay so the 55-watt backup light bulbs I installed don't draw their current through the backup light switch. I will eventually install a relay system for the headlights as well...

*edit* If you've got systems sentry or a lamp-out monitor connecting your headlights this way could cause a "Lamp Out" warning, or it could disable the lamp-out warning system. My car doesn't have this feature so it doesn't affect me, but my old '87 Sport did, and I had to pull the "headlamp out" bulb when I installed the 80/100's.

Re: Headlight Relay Install. What do you think??

Reply #3 – November 10, 2004, 12:30:22 AM

Hmm... guess I was wrong on the headlight switch price. Maybe I was thinking of the multifunction stick on the column.