Swen, I had exactly the same problem a while back, and after a week of circuit chasing with a VOM starting with the horns, I discovered that the ground wire for the horns is actually in the horn stalk itself. A wire comes out of the turn signal housing and penetrates the steel stalk, being soldered to the far side of the tube. The solder joint had cracked and only need re-soldering. The wire was actually a little too short, and there was very little extra to stretch. I wrote up my experiences in the Jan '95 POCA news, which I think is still available from the POCA store.
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