I recall reading somewhere of guys using horn relays to provide extra current for better lites. It sounds like a good approach to me, horn relays have nice sealed cases, mounting brackets, and screw terminals so they can be mounted almost anywhere and they are period correct. I'm thinking of trying this for my brake lite setup. I want to leave the original lite operating through the switch at the master cylinder and run additional lites through relays. But the way horn relays are configured the only way I can figure out how to wire it requires two relays:


Is there a better way?

 

Craig,

maybe I'm reading your schematic wrong ?? but you have the coils of your relays in series right ?? daiseychained. If you lose one you lose them all that way... like old christmas lights... I like the idea and there is an article somewhere on the tech section about doing the same with headlights "Brighter Whites" I think by Steve Delanty.. ANYWAY.. I'd parallel the coil sides of the two relays and that way if one coil fails or a wire breaks, you don't loose all your tail lights..

I'm no wiring genius so I could be all wet here...

john

 

I'm confused. I thought the horn relay was, similar to a starter solenoid in its ultimate purpose, a device that would provide positive switching for the current required by the device. And that, in theory, a horn relay would not be needed if one had a mongo switch mounted on their steering wheel. I assumed that the light switch alone was adequate to handle all the current that the lights draw. I guess if bulbs that needed more juice were used, then a relay would be needed. Is that what you guys are talking about? I

 

I would think that a horn relay would work, but why not just buy a new headlight relay from the parts store? They are only about four bucks, and it would be very fustrating for the old horn relay to go bad in a month. Also, you don't need two relays. Eliminate the one on the right in your schematic. Other than that, it should work fine. You may have got the idea to use two relays from the feature articles on headlights. There are two relays used for headlights because you need one for the dims and one for the brights. I assume that you are doing this relay install because you don't want to run larger wire to the rear to replace the original small stuff. Are your new tail lights normal or led? Led lights draw very very little current. If you are using led, then you may want to wire them without the relay until you can verify if they shine bright enough to suit your tastes. Good luck, John

 

If you use a headlight relay, you only need one relay. The horn relay grounds the horn as you've shown, whereas the headlight relay connects two poles that are not grounded. Horn relay has 3 contacts (one grounded), headlight relay has 4 (also one grounded).