The Stovebolt Site Forums The Shop Area The Electrical Bay 6 volt horn relay

Does the horn relay itself care if it’s positive or negative ground?

I wouldn't think so. Unless it's internally grounded like some starter solenoids are. If there are two connections for the coil (total of 4 overall) then it shouldn't matter.
[on edit]Looking at the '54 wiring diagram, I've confused myself. What are you working on? It shows 3 contacts, marked H, B, and S (horn button).

No

Klhansen, Early ‘40s GMC. I have not removed it yet so I don’t know if it’s marked.

bartamos, that’s what I suspected. Thanks

Are you going to keep it positive ground? I suppose you already know how easy it is to change. All the songs on the radio will play backwards otherwise. Up to you.

It’s not my truck. Just trying to help a friend. The power goes to the relay when you push the horn button (confirmed with test light) but the relay doesn’t click or send power to the horn. Trying to figure out if we can just go to the FLAPS and get any old 6 volt relay or if we have to get a positive ground one. Thanks for the help.

There were no horn relays used back then. They used the two terminal horn. Except for dual horns.

Take off relay. Take to bench. It is probably a 3 terminal. H B S (H orn B attery S witch)

Test in negative ground mode.
1. Apply 6V pos to B with a charger or battery. (6V)
2. Attach volt tester between H and S
3. Ground S to charger neg or battery neg (whichever power supply you use)

Should light the test light


To test horn trumpet:
One terminal horn: Apply 6v pos to terminal and touch horn body to neg
Two terminal horn: Apply pos 6v to correct terminal and neg to other. Don't touch body to either.

bartamos, it is a duel horn setup. I’ll follow the test process this weekend. Thanks

As posted above, the 6v dual "seashell" horn option (1953/1954/1955st) used a relay.

The single 6v "seashell" horn in 54/55st used a relay.

These are the directions showing accessory horn with relay that Tim referenced.
https://www.flickr.com/photos/advance-design_parts_co/11594157364/in/album-72157631868452754/

The subject vehicle is said to be "early 40's GMC". In those years, a single horn had no relay. Dual horn had relay. The dual horns seem to only show up on cars. Anything is possible after many previous owners. All info I see is from Chevy. Assume GMC is the same electrically.
Later on in the evolution, single horns got relays also. In trucks, that seems to be in 1953.

Martin: Not sure how you tested initially, but be advised, on dual horn relay, there is power to relay at all times at "B". Power is sent to "H" when "S" is grounded by horn button. Then the wire on "H" sends power to horn trumpet and back to chassis ground thru horn case/mounting bracket.

Tested both B and S with test light. B has power at all times and S when horn is pressed. H doesn’t get power at all right now. I have jumped directly from a power source to each horn and they honk. Relay is not in an easy location to get at and doesn’t look original. It has a fuse on the side of the housing and the fuse tested good with a multi-meter. I’ve seen this type relay on some Chrysler products but not GM. Relays are cheap so I will just get a 6 volt relay and wire it up. Should work and the gentleman doesn’t care if it’s OEM or not. I’ll have the truck back here Saturday to get er done.

Good plan, sounds like some junkie stuff was added. This is what they sell for 47-54. Says 6V or 12V. Don't know if all relays will accommodate 6V or 12V. Anyway. Chevy got the battery hot for the relay by tapping into voltage regulator battery terminal. But you can get it anywhere. They did not use a fused hot. Put the relay where it's easy to work on/wire up. That is usually on middle or front area of inner fender or on rad crossover. Whatever.

Got a 6volt relay from NAPA this morning. Removed old relay, bolted on new relay and placed wires back as they came off. Horns work perfectly. The old relay and twin horns apparently came off a mid to late 30s Chrysler. Look good on the GMC.