I'm trying to get the cruise control working on my 1987 Camaro. I recently purchased the car so I don't know when it last worked.

so far I've checked:
That the Fuse is good
Vacuum supply to servo is steady
Brake vacuum dump switch dumping vacuum when brake is pressed and holding when not pressed
3rd brake light all working
A known working servo from my S10
3 different cruise control stalks I have laying around.

Any idea where to look next and any diagnogstic procedures?

 

I checked for power at the servo and got 8v between the B & D pins as mentioned in a article I read.

 

Does the 1987 cruise module cross over to other 1980s' cars that I could try and find at the auto wrecker?

On the brake pedal assembly, is it only the switch with the vacuum dump that signals the cruise module? Is this switch normally open or closed? I could test it.

 

I got a cruise control module out of a 1985 V6 camaro. I put it in and the cruise works. Although at lower speeds it seems to hunter up and down. Ill be going 50kph and it will slow down to 45kph then speed back up to 50, then drop to 45 and up to 50 over and over.

Is the V6 module different? Is there an adjustment in the Servo linkage?

 

It seems possible the v6 module is faulty. Anything that old from a junkyard is suspect. My guess would be look at the electronic "eye" mounted in the back of the speedometer. This electronic eye senses speed at the speedometer, and I can imagine it causing trouble with the system hunting for exact speed. I believe any junkyard one should do from any GM up to around 1987.
Removing the instrument cluster to access the speedometer and other gauges is actually pretty easy, and once you have done it once can do it again in 15 minutes. Don't try to squeeze your hand under dash, just remove entire cluster. Take your time the first time and go slow so as not to break things or miss a nut/bolt.
The eye has one tiny bolt holding it into back of speedometer. It has wires running to a yellow junction box with the letters "AC" on it.