QuestionScott. I have a 1974 Spitfire. My horn relay seems to be dead. Bought a new relay from major parts supplier. The original relay has 3 prongs(4 if you include one terminal having two prongs,but only one wire goes to that connection).My manual gives the position of where wires go C1 purple yellow wire,purple wire C2,purple black wire terminal W1- BUT replacement Lucas relay has numbers on it ?? 87,86,85, 30/51. Have no idea where to connect wires. Called parts supplier and they were clueless even though they sell the part.
Answer
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first figure out if your horn wire needs +12 or GND to make the horn work.
I usually pop the plastic cap off the relay to see which wires are the magnet for the closing the switch, and which two wires are the switch.
Horns are usually GND triggered, so I suspect that if your old one was metal cased, that's why you're missing a wire; you would end up taking the other side of the relay switch terminal and wire it to gnd.
What you have is a generic BOSCH relay, and a wiring diagram is at a link below.
http://www.bcae1.com/relays.htm
Use a volt meter, figure out which of your existing wires, is +12, GND, and you should be almost there.
