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I've been trying to get the horns to work on my P15 - they did not work at all. So I ran all the procedures in the service manual for diagnosing a horn that won't sound. At each diagnosis step, the horn sounded or the lights on the tester lit up; in this case, the manual says to replace the horn relay. So, I've replaced the horn relay with a NOS one just like the one that was in the car. Now, when I turn the ignition on, the horn sounds continuously and stops when I press the horn ring down on the steering wheel. So, I guess it did need a new horn relay! The wiring diagram shows 4 lines into or out of the horn relay: - Wire to the horns - Wire to the negative ignition coil terminal - Wire to the horn button - Wire to....I'm not sure how to read this last one. In the diagram, the last wire goes across the big black cable that goes from the battery to the solenoid switch; the wire line passes very close to the solenoid switch and then goes on to the ammeter. On my car, this last wire is connected from the B terminal on the horn relay directly to a post on the solenoid switch, and the big battery cable is connected to the same post. And, I have a fifth wire connected to the same post as the negative ignition coil wire. This fifth wire joins a bundle of thick green and red wires that run back through the firewall. I tried disconnecting this fifth wire just to see what happens, but then the horn doesn't work at all. And, the hood ornament light no longer comes on when I turn on the ignition. Thoughts? Is the extra wire the positive ground perhaps? I'm wondering if the extra wire is some hack to get around the old broken relay so that the car would start. But it doesn't look like a hack wire since it seems to be the end of a legit wire that runs back with other legit wires back through the firewall.