I was looking at the electrical diagram for the sedan (the coupe works the same way) and it shows the horn has one wire which goes to 12 volts via the fuse block and the other horn wire goes to ground via the horn ring on the steering wheel. Here is one way to tackle the task:
1) verify the horn works. You can disconnect it and then connect it across the battery to see if it is working.
2) For the sedan, the white / blue stripe wire going to the horn goes to 12 volts via the fuse block. If you measure the voltage at this wire (put the + lead at this wire and the - lead to the battery negative or chassis ground), you should see 12 volts. If not, you may have a problem at the fuse block or a problem in the wiring to the fuse block.
3) For the sedan, the blue / red stripe wire goes to the horn ring. So, if step (2) is ok, you should be able to connect one side of the horn to the power with the white / blue stripe connection and ground the other wire from the horn. Doing this, the horn should operate.
4) If step (3) is ok, you can connect both wires to the horn and chase down the wire which goes to the horn ring. If you ground it at any point (including at the horn ring), the horn should operate if the wiring is good. You can take a wire which is clipped to chassis ground on one end and use the other end to touch different points in the circuit to make a ground connection.
My experience has been the horn is defective or the grounding contact at the horn ring requires cleaning to allow for proper grounding.
good luck,
Dale
> This leads me to the next issue - my horn hardly ever works. Is there a "good" method to troubleshoot this?