Shorts out is a good word, but all it is really doing is closing the circuit for the horn. That is why is an insulated bushing/gromet on each of the 4 bolts for the horn plate. Common complaint on old 4 spoke wheels.
Porsche does not sell just the bushing. You have to buy the entire plate.
Disconnect the battery and remove the air bag. 4 bolts for the plate. One guy sliced a thin section of garden hose and used that as an insulator. You might also find something in the plumbing department.
