Classic/Antique Car Repair: 1977 Plymouth Gran Fury Brougham, plymouth gran fury, radiator core

Question
I am trying to locate the horn relay on this particular car. I tested the horn by straight wiring it to the battery and it works perfectly.  I also checked all the fuses and they are all in excellent working order. The horn does not work when I press the steering wheel "button". I am guessing that it is the horn relay that is bad. Could help me locate the relay?

Answer
The horn relay could be the problem, but more likely it is a bad connection inside the steering wheel horn switch.

To find the horn relay, follow the wires that come from the horns back to a small metal can that is mounted on the radiator core support, probably on the driver's side of the car near the left inner fender.  The relay is about 1 inch by 2 inches, and about 1 1/2 inches tall, with 3 wires going to it.   The wire terminals are marked H, B and S.  The H terminal is the one that goes out to the horn.  The B terminal goes to a source of 12 volts, probably under the dash somewhere, and the "S" terminal is the one that is grounded by the horn ring when you press it.  To test the relay, run a separate wire to this "S" terminal and tap it on the negative terminal of the battery - if that makes the horns blow, the relay is fine.  

Inspect the wiring that goes from the "S" terminal back to the steering column.  The wire may be unplugged or broken, but most likely the problem is going to be found up inside the steering wheel.

Take the steering wheel hardware apart and troubleshoot the electrical contacts that ground the horn wire.  If you have to pull the steering wheel to get at the contacts, you will need a special puller for it - your tool rental place should have one.

If the problem is inside the steering wheel or column, and you don't want to get involved in taking that all apart, you can make a temporary fix by running a different wire from the "S" terminal on the relay to a new horn button which you can buy at the parts store.  Just wire it up to connect the "S" terminal to ground when you press the button - that will give you a functioning horn if you need it to get past inspection.  

Dick