Faqs By Headlight Relay

Why does your headlight relay only have two relays, shouldn't it have four?

Our relay system provides the same level of redundancy as the original headlight circuit. The factory wiring runs a single wire from the headlight switch to the fuse box for the low beams, and another wire for the high beams. We tap into these two wires before they split at the fuse box to feed all 4 lights. A relay is considered at the same likelihood of failure as a switch, since the contacts are by far the most common failure mode of either device. Two 100 Watt bulbs draw about 15 amps, so each 40 amp relay has no problem with the load.

Why aren't the relays fused?

Fusing relays is not the convention for automotive wiring. The relay is considered the same as a switch - the likelihood of failure to short is extremely low compared to a load device. Our system retains the factory fuses for each individual light element. ------------------------------------------------------------------------------------------------------------------------- Note that the main battery cable runs all the way back to the starter and feeds are running all over the car including to the alternator, ignition switch, and finally back to the fuse box with no fuses. --------------------------------------------------------------------------------------------------------------------------- If fusing is desired for the power feed portion of the circuit, it would be more appropriate to apply it to the entire set of feeds with a maxi-fuse or similar. This is the method applied to many newer cars. This would encompass all the small wires currently attached to the battery positive terminal, and to maintain this level of protection you would also have to consider protecting the wires from the starter to the alternator and the B+ output from the alternator. --------------------------------------------------------------------------------------------------------------------------- There are two circuits where the factory was remiss, the gauge lighting and the AC condenser fan are loads that were not fused, and adding inline fuses to the circuits would be a good idea.

What relays are used?

The relays are the most common universal relay, often referred to as "cube" relays or "Hella" relays. Nearly every auto manufacturer has used this type of relay at some point, from fuel pumps to horns, so replacements can be found anywhere with little trouble. A 4 or 5 prong version can be used as a replacement. We deliver our sets with Tyco (Bosch) 40 Amp relays, which should last the life of the car.