1986 Chevy Caprice Classic Horn not working

Diagram should be on the inside of the fuse box or relay cluster lid/cover. If Test light has 1 wire and a sharp tip? Yes, but only if you push the horn button too ;-)

My guess is that the horn lost its ground, but you can check this with the light. The horn only beeps when both GROUND and Pos 12v are present. The horn button gives the relay 12v to close, and the relay gives the horn 12v to operate. The ground is always connected.

Connect tester clipwire to 12v source (battery, headlight (has to be on) and touch its tip to metal of car. Does it light? Good. the tester is working and the 12v is a good source.

Touch one of the 2 horn connection or wires (poke it thru the plastic - why tip is sharp). Does it light? Touch the other, does it?

If both light, (1 will be brighter) we can assume the horn coil is good and it is getting a good ground and I was wrong (it happens... but not often). The side that is BRIGHTER is the ground wire side.

Now have someone mash the horn button. Do you hear a tiny click? That is the horn relay. If not, look for the horn relay fuse and replace it. If you DID hear the click, the relay coil is good and is trying to switch 12v to drive the horn.

Now is time to locate and replace the horn fuse or the relay may have bad contacts. Look at the other relay part numbers in the cluster and see if there is a match for the horn one. Swap it out and try the horn.

Hope this all helps. To 'test' the horn, touch the dim side again anf listen for a scratching sound. That is the 12v going thru the tiny bulb in the tester (a resistance) and trying to drive the horn.

Good Luck!