Brighter Headlights Using Relays


Headlights at night

This quick article plays to the use of relays to get a brighter headlight by unloading the headlight switch and using a pair of relays to trigger the power to the headlights. This is a major fix/upgrade to early cars that came with incandescent lights and you want to upgrade to a halogen based unit. The problem is that they draw more power. You couple that with the fact that most dash mounted headlight units were fused or relayed internally to handle the original power needs. What would happen when you updated the lamps is not immediately apparent. But if you had your lights on for any length of time they would “wink out” because of over heating the switch. If it was a relay style they would come back on once they cooled down. If it is a fused style you may have to pull the headlight switch out of the dash to replace the fuse. Neither one of these is a good scenario. Mainly because you had the lights on because you needed them, like for driving, at night! Bad! Bad!

This is the fix guys and gals. I have done a few of these and the results are nothing short of spectacular. It also cures the phenomenon of the lights dimming at idle on many of the early cars with generators.

Basic headlight relay wiring

Basic headlight relay wiring

The diagram is a simple schematic on how to set up your headlights so that both high and low beams get a full 12 volts. This results in brighter lights and better night vision.

The original wires for the headlamps are tapped at the red dots and the new feeds come from the relays at the blue dots. The relays should be a units with a capacity for 30 amps or more.

4 pin relays are pretty common and a few of the choices are

  • Bosch 0332014157
  • Four seasons 35989
  • Sorenson 41-5118
  • GM 15515693

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