I have a 91 Honda Civic DX 1.5 aircondition disconnected, cruise control not used
But the switch lights up. Problem, this is not the original 1.5 engine. The vehicle
Itself has nearly 350,000 miles on it.
After replacing the distributor, the Idle is high in the mornings,(normal).
But some how it affected the brake lights.
Tail lights no problem. Replaced the light switch, no brake lights, can't take the
Car out of park without using a fingernail file, (metal) to put it in gear.
I thought the shiftlock solenoid was the problem but honda don't make the part
Anymore. After checking the solenoid, its OK, no resistance.
But on the fuse block(passenger side under hood, the second fuse was blown.
I replaced the clip from another 91 civic, it worked well for a couple of days and
The fuse blew again. When the car is warmed up, it idles fast, around 7-10 rpms.
While the same fuse keep blowing, I think the problem is related to the EACV, the two prog device you disconnect when you set the idle speed.
Why do I think this maybe the problem? I can replace the fuse, warm the car
Up and drive it and I have brake lights.
But soon the brake pedal is firmer, the engine idle speed goes up, and in seconds goes down again and again and when checked, no brake lights, and
A blown fuse. Since the brake light switch is new, the other one must have been fine too
So I think this is a problem where more than one components share one fuse and share two ground points.
If you have an answer, please let me know.

EACV if I remember right is the idle speed control... its basically a solenoid that controls air leak past the throttle body to regulate idle speed.

I've had to replace one on mine... its really not something easy to troubleshoot short of replacing it.