Does anyone know what fuse controls the horn and where it is located ?

  According to my 1992 service manual (most C4s are similar) the horn fuse is located on the right hand end of the dash near the passenger's door.  The fuse you are looking for is a 15-amp fuse labeled THEFT.  The steering wheel horn buttons activate a horn relay located below the right side of the dash just above the bottom cover (knee bolster) near and below the back of the fuse cluster.  This relay simply closes the circuit between the fuse and the horns.  The relay is also triggered by the Central Control Module for use by the Security System, but that probably won't be a factor in your problem.  The wire color between the fuse and the relay input is orange.  The wires from the relay to the horns are dark- green color, and go through just one connector C100 located in the left hand side of the bulkhead connector into the left engine compartment.  Finally the wire from the horn buttons to the relay are black and pass through the C204 connector located on the right side of the steering column. 

I'm quite sure the horn circuit in your '87 is the same as the circuit in my '84.   The fuse for the horn is the CTSY/CLK fuse.   If that's bad, you would loose a lot of other things, too!   The horn relay is behind the center panel in your dash.

I have replaced the steering wheel in my '84 with a '87 wheel, so I've tried both the '87 and the '84 horn buttons in my "new" wheel.  The '84 button fits my '87 wheel just fine, and in fact, I prefer the '84 button over the '87.   I'm going to guess that you have rust in your contacts inside your horn button.   The button comes off with a little prying around the edge.   There is a wire from the horn button to the slip ring contact that removes by pushing down on the sleeve and twisting the sleeve CCW (like removing a light bulb).   Caution: The sleeve is delicate.   If you ground that wire your horn should honk.

 7/7/17 Correction:  Brain fade!  The steering wheel I installed on my '84 about 12 years ago was from an '86, not an '87.   My suggestions may be all wrong, but hopefully will be similar.

|UPDATED|7/7/2017 10:18:32 PM (AZT)|/UPDATED|

Thank you !

Thanks for the advice.  I am back working on my car this week and I will follow your advice.

Listen for the horn relay to click when you press on the horn button. No click could be no contact on the button, bad fuse, or bad relay. If you do hear a click, then the fuse, and button contacts are good, and you would go for the relay at that point. Just because the relay clicks does not mean it is making contact on the horn circuit(from relay to horn(s))

The relay that operates your rear hatch is the same relay for your horn so you can swap them out to do a quick test if you don't hear it click for the horn test both of them in the hatch it could be a wiring issue like what was on my 84

6 years later & a 88 vette.  After all the troubleshooting, found out it was horn button. Popped steering wheel horn button off & The wing like metal pieces on inside of button (3 & 9 o’clock) were not grounding/making contact with the inside part in steering wheel. I pulled the 2 pieces that are inside the steering wheel inwards so that it makes contact & allow the button switch to work.    Before adjustment: Relay worked, all fuses ok, horns worked

|UPDATED|1/3/2023 3:40:58 PM (AZT)|/UPDATED|