How to find a short in a horn

Granddaughters 1996 Ford Escort, horn works when engine is off, but not when you put the key in the ignition. Ford, and Car Forums offering little help. I thought it was air bag related (turns out that's a 1997 problem), and wasted $54.00 at a salvage yard.

I have found some references which say it could be a short, or ground problem in the steering column. How do I go about finding such a short or ground problem?

Any other ideas?

I do have a diagram of the schematic for the horn itself.

Thanks, Gary

You need to start off with a wiring diagram. Chilton's manuals would be a good place to look. Trace the problem wire back using the diagram.

One side of the horn is probably grounded through the clamp, the other side would have the short to +12V. If both sides are run in the diagram, one is probably intentionally connected to +12V, and the other would have the short to ground - this will probably return to a low side driver on a controller board. This could be a shorted drive transistor, save yourself some time and start at that point - the connector on the controller board.

If it IS the controller, you can get a rebuilt unit and just pay the core charge like with an alternator.

If all your other devices are working properly, just rewire the horn lines. Leave the current horn wires as it is but just disconnect them. It will save you a lot of time but if you want to trace its problem, go on..