1988 5.0 cruise/horn

Just checked my '89 and the horn and cruise are on differnt circuits, so you have two issues. Check the fuses first.

On my '89 the fuse for the horn would burn out every time I tried the horn. Turned out both horns (behind the driver side headlight in the fenderwell) were shorted. Purchased and installed replacements (and a new fuse) and its been fine. Have not had any issues with the cruise control yet (at 171,000 miles its still works ok).

hank phoenix

There's a couple of things to check. First off, if your steering column has any kind of rubber insulated "rag joint" under the hood, then there is a little piece of metal that jumps the rubber. In the past, this joint was prone to corrosion. A simple way to check if this is the problem is to remove the horn pad and grouind the end of the steering shaft. If the horn button works after adding this ground, the cruise usually will work as well. Of course, you then need to fix the ground permanently.

Next, check the horn relay. When you have factory installed cruise, there is a horn relay which also provides current to the on-off switch so it can turn the cruise module on and off. If the solenoid in the relay is open or it's not receiving power, then the cruise control can't initialize. Finally if this doesn't work, pull the steering wheel and check the two brushes contacting the race tracks under the streering wheel. It's possible one is worn to the point it no longer contacts reliably.

Keep in mind this advice probably will not work for the airbag equipped Mustangs of later manufacture as they lack the brushes in the column and have a clock spring tape instead.

As far as I know, the horn relay is the only common point between these two circuits.