Relay Harness

[87GrandMarq]

Does anyone make a headlight relay harness on here? I could do it myself but with my luck something will fail lol.

I bought an H4 harness a while back but the wiring seems thin and the relays aren’t bosch style so I couldn’t just run out and get another one if one broke.

[sly]

this one uses standard bosch style relays: https://www.amazon.com/4-Headlight-W.../dp/B06XJ771YQ

The wire is even thinner than stock Ford wire though, so I wouldn't order this one. I can't find one that uses 12AWG wire though.

Painless Performance makes a kit using better quality parts, but it's still H4 and not 4656... https://www.painlessperformance.com/wc/lv.php?sl=30814
or on Amazon: https://www.amazon.com/Painless-3081...dp/B002Q34P4Q/
but it's expensive (made in Fort Worth, TX though)


They're wired for H4 and not 4656 though. So you could either repin the 3-wire connectors or swap out the stock sealed beams with H4 sealed beams or other conversion housings.


This is why I made my own relay "splice" and tapped the wire harness on the driver fender, cutting the low and high beam wires, using those as the coil trigger wires and then the output from the relay to drive the headlamp side of the cut wire. Run the other side of both coils to a nearby fender bolt for ground and run a fat power wire through a 25A circuit breaker from the common on both relays to the battery.

Then you can just order a pack of relays with wired sockets like these:

https://www.amazon.com/Hamolar-Pack-Relay-SPDT-Harness/dp/B093GMF6M1/

I used one of those bolt on circuit breakers: https://www.amazon.com/Bussmann-CBC-...dp/B001PYSU4S/
add some ring terminals and some 12AWG wire to run to the relays... and you can build your own.

[87GrandMarq]

Screw it I’ll just make a set given the price of the harness. The headlight connectors I’ve seen at the auto parts store seem like they have crappy wiring too though. Any suggestions there?

[kishy]

It's far from the best way, but what I do is just cut the low and high beam wires near the front of the driver fender, and use the ones coming from the dash to trigger the relays, and the ones going to the lamps as the output. The only new wires I run are the battery positive wires, with fuses, and the grounds for the relays.

This takes the headlight switch out of the picture and does improve the light output. It's less invasive but also less thorough. Depending on what problem you're trying to solve, it might or might not get you to a solution.

[87GrandMarq]

I don’t have any problems and I’d like to keep it that way. I don’t drive the car much but I want to avoid burning the headlight switch harness if I can. Also I’d like to build a plug and play harness. I know it’s not a big deal but I don’t like cutting the stock wiring if I don’t have to.

[gadget73]

I have one of those really cheap ones on the Continental, and honestly it works great. Its not thicker than OE wire, but there is a better than 2 volt difference between the relay harness and the stock harness. Been on there for 4 years and have not had a single issue with it. Still using the cheap Bosch-type relays that came with it. It looks like a complete piece of shit, basically like what you'd expect a $20 harness from China to be, but I can't argue about the results. I did put some spark plug grease in all of the connectors to try and help it along but thats it.

Bonus for me at least, the car's wiring is absolutely un-modified so if that harness catches on fire I can just plug the stock connectors in and go. I really don't want to cut anything because it makes it impossible to easily bypass for troubleshooting.


just a mention, the pinout for H4 and the sealed beam lamps is not the same. the harness I bought was supposed to be wired for H4, but it was actually wired for sealed beams. Just make sure you check it closely before plugging anything in. You flip 2 of the wires, its not a big deal.

[87GrandMarq]

Great info thanks Gadget. That’s what I have, maybe I’ll run it and watch that it doesn’t start burning. Eventually I’ll make my own though.

[gadget73]

The one on the Towncar I made, its heavier gauge, but I had to recycle some old headlamp sockets so there is about 6" of wire at each light thats thinner gauge. Same at the relay sockets. Overall I don't know that it really works any better. The ideal way to do it would be to find the sockets and bare terminals and just make your own that way, no splices to thinner wires.

[GM_Guy]

Bypassing all the wiring running back and forth to the headlight switch is a big improvement in itself. 6' of wire from the battery to relays & headlights vs 10'+ running to the headlight switch and back to the front. 87' take some voltage readings at the headlight (engine running) (and at the battery) before you pull everything apart. Compare after, you'll be pleasantly surprised.

[87GrandMarq]

I’ll get some readings maybe this week sometime. The car sits at my parents house not so close so I don’t get to wrench on it often anymore. I’ll probably take some measurements while I’m there and start collecting parts to build one at my apartment.