I am installing a set of air horns on a 1994 940T. When I wire up the horns as indicated for a car with a grounded horn button the compressor activates.



When I connect the wire (85) that I have spliced into the existing horn wire (yellow on car) the relay closes and the compressor activates. When I put a meter on this wire there is no continuity to ground unless the horn button is used to complete the circuit (as you would expect). So it does not show continuity to ground with the meter but is providing a ground for the compressor. If I simply attach a wire to 85 it will activate the compressor when grounded.

I have installed these horns before on Volvos. If you notice the smudge in the diagram connecting the 12v source to 30 it is because there is a misprint in the diagram. I found that out several years ago trying to install identical horns on a 740.

So the question is why does the wire spliced into the yellow horn wire on the car not show continuity to ground (unless the horn button is pressed) but yet provides a ground for the compressor?

Thanks for you help.

Randy