Pablos49,
I don't know if your truck used a horn relay...I don't think it did. If it didn't, the horn would have two wires, one from the system power and the second for a horn ground supplied by the horn button.
If the horn is powered properly, you should be able to jump the other terminal to a good clean ground and get the horn to blow.
If this happens, it means the wiring or horn button proper is faulty. If it doesn't happen, it means the horn is no good or the wiring to it is loose or poorly connected.
It's possible to use regular jumper cables connected directly to the battery to test a horn. This takes any loose connection or poor ground out of the equation and can sort of knock the cobwebs out and get the vibrator working again.
If your '49 used a horn relay this procedure isn't applicable.
Stuart
