I have a 1938 Plymouth truck have the original horn and Purchased a horn regulator from NAPA suppose to be the right one??? Has 3 connections on the regulator and 2 on the horn.Is one to connect to the horn button, one to one side of the horn and one to the otherside of the horn??? ???Thanks for the help Matt
"Regulator" or relay?
Typically the horn is connected to a hot lead from the battery and then the other connection is grounded to sound the horn. High power or dual horns usually draw too much current to ground the horn through the horn button so they put a relay in. The relay grounds the horn when the control wire from the horn button is grounded by pressing the horn button.
You don't list the car you are working on and none is listed in your profile. If you give the year/model I bet someone on this forum can come up with a wiring diagram and help you figure out where each terminal on that device is connected.