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Discussion Starter #1
Hey all, picked up a 75 nova recently and am having one issue. The horn does not work, ive tested the horn itself and it works fine, but when I try to use the horn button at the wheel, nothing. This leads me to believe its either the relay or the wiring.

1. Where's the horn relay on a 75 located? I see where the horn wire hits the firewall but can't trace it from there without removing the brake booster, and would rather not if I don't have to.

2. Anything else to check if it turns out the relay is fine?

Thanks for the help!
 

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Welcome!

The horn relay is located up under the dash, right above the fuse box. It has a cube shaped plastic case and a 3-wire connector with a red, green, and black wire.

The red wire is a power feed that should be live all the time. The green wire is the one that passes through the firewall bulkhead connector and runs out to the horn. And the black wire goes up through the steering column to the horn button (which completes the circuit to ground to activate the relay).

For testing purposes, you can temporarily ground the black wire at the horn relay (do that by backprobing the connector while it's still plugged into the relay). If that makes the horn blow, the problem is most likely in the steering wheel horn button or contact ring. Or a bad connection or break in the black wire somewhere between the relay & button.

If temporarily grounding the black wire at the relay does nothing, it's most likely a bad relay. But it wouldn't hurt to first check the red wire to make sure it has power before replacing the relay.

Also, if temporarily grounding the black wire at the relay just makes the relay click, that would indicate either bad relay contacts or a break or bad connection somewhere in the green wire between the relay & horn.
 

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Discussion Starter #3
Welcome!

The horn relay is located up under the dash, right above the fuse box. It has a cube shaped plastic case and a 3-wire connector with a red, green, and black wire.

The red wire is a power feed that should be live all the time. The green wire is the one that passes through the firewall bulkhead connector and runs out to the horn. And the black wire goes up through the steering column to the horn button (which completes the circuit to ground to activate the relay).

For testing purposes, you can temporarily ground the black wire at the horn relay (do that by backprobing the connector while it's still plugged into the relay). If that makes the horn blow, the problem is most likely in the steering wheel horn button or contact ring. Or a bad connection or break in the black wire somewhere between the relay & button.

If temporarily grounding the black wire at the relay does nothing, it's most likely a bad relay. But it wouldn't hurt to first check the red wire to make sure it has power before replacing the relay.

Also, if temporarily grounding the black wire at the relay just makes the relay click, that would indicate either bad relay contacts or a break or bad connection somewhere in the green wire between the relay & horn.
Thanks a ton Ray! Went looking through the loom and figured out why I couldn't find the relay, it's not there. So I guess I'll start with getting a replacement and hoping for the best, otherwise I'll follow the steps you gave. Really appreciate it!
 

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You're welcome!

They're a fairly common relay (Standard Motor Products #HR151 or equivalent) that should be available at most auto parts stores.

Yeah, hopefully just replacing the relay will do the trick. But the fact that someone removed it could be an indication that there are other issues. For example, they might have had a problem with the horn sounding continuously and removed the relay to stop it. If that's the case, it could be due to a stuck horn button or a short to ground somewhere along the black wire.
 

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Discussion Starter #5
They had also cut the green wire in the engine bay going to the horn, so who knows. I've put in a new turn signal switch, and am putting a new steering wheel and horn. Picking up a relay after work today so hopefully is an easy fix.
 

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If someone took out the horn relay, and then went so far as to cut the green wire, I bet they had a reason for doing so. Granted, it may have been a bad and misguided reason, but my point is that maybe you should trace out all the wiring related to the horn and do some extra checking to make sure everything is OK. Someone may have put a band aid over a problem that you don't want cropping up again.
 

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Discussion Starter #7
Welp, followed the wires and there were no breaks before or after the firewall. Installed a new relay unit and the horn works like a champ. Thanks for the help and the suggestion to double check everything!
 
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