[Mickey_London]

1970 Firebird



My horn has never worked since I bough the car, and traced it back to relay


I have bought a new relay, same as the old one, 893-12V

But when I plug it in my horn is constantly blowing

I have checked the wiring from the steering wheel and there is only a ground when the horn centre is pressed down. This, I think is correct, as when you press the horn centre it then Earths out and completes the circuit.
Perhaps an expert can correct me if I am wrong

I even stripped everything back, took out the horn contact cam, and it still sounded the horn constantly

To me, it is as though the relay is stuck on, feeding the black wire down to the horn with a constant 12v

I have an old battery in my garage, so I connected the relay up as follows

Picture for reference


I put a 12 volt feed, from the positive pole of the battery, to the terminal with the red spot

Then put my volt meter between the terminal with green spot to the battery negative post and I get 12 volts

I then put my volt meter from the terminal with black spot to the battery negative post and again I get 12 volts


Are these readings correct

Thanks for any replies

Mick

[Peter Serio]

Here is the basic circuit of how all GM car horn(s) are wired thru the relay. NOTE: the metal mounting (screw tab) surface of the relay is an electrical ground for the coil inside.

[Mickey_London]

So could it be that because I didn't screw the relay to the bulkhead it wasn't grounding out
Will try again in the morning
Will post back with the result
Thanks for the reply
Mick

[Peter Serio]

Right, the relay has to be grounded to complete the control circuit. The coil controls the current from battery + to the horn= high amperage. The steering wheel contact is a low amperage control for the coil. Same deal as the relay mounting bracket the metal mounting bracket for the horn is a ground as well.

[Bill Hanlon]

Not grounding the relay frame shouldn't have anything to do with the horn's operation.

12 volts comes into the relay on terminal A, shown on the left in this drawing. It connects to one contact of the relay and to one end of the relay coil.

The other end of the relay coil exits on terminal B and attaches to the horn button contact. When the horn button is pushed it grounds that end of the relay coil which pulls in the relay allowing current to flow through the relay contacts and out the third relay terminal C to the horn.

I don't know which terminal is which on your relay, which is why I marked mine A, B and C. You need to understand which is which on your horn relay.

I can't find a 1970 Firebird wiring diagram online that isn't virus infected, so maybe someone on this forum can provide one.

[Chris65LeMans]

The horn in my ‘65 works when the horn button grounds to the steering column. Once, I had a metal shaving in there that was making it blow constantly.

I suspect that the problem is in your horn button. I’d pull the wheel to have a look..

[Geoff]

Agree with Bill, relay case does not need to be earthed & will make no difference if it is.

Most likely cause of the problem is wire mix up on the relay terminals.

[Mickey_London]

On my picture above the terminals are
RED- ----- 12 Volt feed
GREEN -- Up to horn push on steering wheel
BLACK -- Down to Horn Sounder
PINK ---- Up to the ignition switch, this is so you get a buzzing sound when the key is in the ignition

So what I did this morning is
Screwed the relay to the bulkhead
Then fitted the 12 volt wire to the terminal RED
I then, with a piece of wire from my garage, fitted it to the BLACK terminal
As soon as I touch the Horn terminal with this piece of wire, the horn sounded

So even with the horn push out of the picture the horn still blows
I think my new relay is faulty and stuck on
Does this sound right

Thanks again for all the help Guys
Really appreciate it
Mick

[Mickey_London]

Sorted

I took the cover off, to expose the electrics inside the new relay
What I found was the arm that feeds the Black wire to the Horn sounder was bent down, which made a permanent 12 Volt feed to the horn sounder
So bent it back to release the contact.

Plugged it all in and Bingo

Thanks again for all the suggestions
Mick