Check the pressure sensor on the master cylinder - very common.
Check 15 amp fuse "R" in the fuse box. It appears that the horn relay feeds part of the cruise control system.
If the cruise control on your 1987 300ZX does not work, you might have an issue with the cruise control fuse or wiring. You could also have a problem with the switch that turns the cruise control on and off.
cruise control does not work on 98 astro van
The horn relay and the cruise control steering wheel switch are powered from the same fuse. Check fuse #44 at the inside fuse panel under the dash.
Cruise will NOT work if the speedometer has a problem
the crusie control band is probly broken
Hopefully, you have had the cruise control module recall work done. It's free at any Ford, Lincoln or Mercury dealership. It can start a fire and be very dangerous. Take it to dealership right away.
Have you tried pressing the cruise control button on the dash?
cruise control does not work when headlights are on
My 08 GMC Sierra has Active Fuel Management, and it does work while using cruise control.
You probably need to install a new cruise control component.
check fuses then refer to the speed control sensor which is on the throttle body closest to the air intake hose that controls the engine idle and speed control. Good luck.