Headlight Relay Modification

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By AMC Eagles Den Member John Bendiksen

I am posting this to encourage anyone who has not added relays to their headlight circuits to do so. It's a quick, fun project that makes a huge difference in your headlight brightness.

When I first got my Eagle, I was dismayed to see how dim and 'yellowy' the headlights were. It was so bad that I hesitated to drive it much at night. At first, I blamed the old-school small rectangular headlights. I replaced them all with halogen units, and they actually seemed a little worse. Then I did some research on this board and elsewhere, and learned that AMC did not use relays for the headlights (in 1984, at least); the entire current for all 4 headlights runs all the way from the battery to the headlight switch on the dash and back to the lights themselves! I looked at the wire on the headlight side, and it was very thin gauge, I'm guessing 18-gauge at best. I wish now that I had actually measured the voltage drop at the headlights themselves (for a before/after comparison), but instead I jumped right into the relay project.

I used this article as a guide for the project: http://www.danielsternlighting.com/tech/relays/relays.html Although it is not Eagle-specific, it explains the benefits of adding relays to older cars very well, and has lots of how-to information.

I bought a couple of relays (Metra Install E-123 Bay Tyco Relay 12 Volt 30 Amp, $6.45 each on Amazon), a spool each of red and black 14-gauge wire, and a inline fuse block (In-line ACT Water-resistant Fuse Holder - 10AWG, $3.05 on Amazon). If you buy some other relay type, make sure you get the kind that have two output terminals, so you can run a separate line for each headlight. I started out wanting to use sockets for the relays themselves, but all of the ones I could find used thin 16 or 18 gauge wire for the leads, which would have defeated my purpose. So I ended up going with regular 1/4 inch female terminal connectors, which I soldered directly onto the wires to the switch and lights.

To keep all of the wires as short as possible, I mounted the relays on a wooden block very close to the battery. I grounded the relays and all four headlights (14-gauge black wires) to one of the mounting screws for the small metal thing (relay?) mounted right behind the battery. I used individual wires for power to each headlight (14-gauge red wires), running directly to the relays. Here's a picture, looking over the fender from the passenger-side corner into the engine compartment:


The thick red wire loop is the 10-gauge positive feed (with 40-amp fuse) for the whole system

The difference this made was amazing, literally like night and day. The 'yellowness' is gone, and the lights are much, much brighter. And I have to think it's a little safer to not have the full lighting current running up to the headlight switch on the dash.

John Bendiksen