1989 GMC Sierra....cruise control question

This truck doesnt seem to have any kind of vacuum for the cruise unit. It has an electrical unit mounted to the fire wall, near the brake master cylinder. It is hooked up to the accel portion of the TBI, all the elect wires are connected and all the fuses under the dash are good.

My cruise dont work.....I think that is the obvious reason for posting and I just wanted to know exactly all the components there are to the cruise on this truck and what to look for when cruise control does not operate. There are no lights on my dash to prevent cruise from working....brake, check engine...etc.

Ignition in RUN position, Cruise Control Switch ON

Brown wire at Cruise Control Switch should be 12 volts. Test light should light with other end connected to ground. If not, check fuse "GAGES". Could be bad brown wire.

Grey wire at Cruise Control Switch should have 12 volts. If not replace switch.

Grey wire at Cruise Control Module (under hood) should have 12 volts. Else bad wire from Cruise control switch.

Connect volt meter or test light to Grey Wire and Black/White Wire at Cruise Control module. If not, Black/White wire is not conected to ground. Fix wire.

Connect meter or light from Grey wire at Cruise Release Switch to ground. If not 12 volts, repair Grey wire to Cruise Release Switch.

Test Light Blue wire at Cruise Release Switch to Ground. If not 12 volts, replace Cruise Release Switch.

Test Light Blue Wire at Brake Switch to ground. If not 12 volts, fix Light Blue wire.

Test Brown wire at Brake Switch to ground. If not 12 volts, replace or adjust brake switch.

Test Brown wire at Cruise Control Module to ground. If not 12 volts, fix brown wire between Cruise Control Module and brake switch.

The cruise control release switch is very close to the brake switch.

//2000CAYukon

I checked under the dash, all around the brake pedal and found the brake switch.....located directly above that is another type of switch that moves with the brake pedal. I checked every where else around there and found nothing else that would be any kind of brake release switch for cruise.

The wires on the switch mentioned go from top to bottom....Brown, Lt. Green, Pink, Purple, Orange and White. The brake switch itself has two wires...White and Lt. Green. There was no Lt. Blue wire to be found. I did check the Brown wire at "assuming" the cruise release switch and there was no voltage. There was also no voltage at the brown wire on the cruise module. All other wires/tests turned out good.

If the brown wire at the cruise release switch requires 12 volts.....can I pull the voltage from the Lt. Green wire on the brake switch and apply it to the Brown wire? When the brake pedal is depressed, the Lt. Green wire looses voltage on the brake switch.

This info is out of the 1990 factory manual so I should have told you that up front. I guess they changed the wire color from 89 to 90.

For 90, the cruise release switch only has 2 wires, Grey and Light Blue. So what you found is probably the cruise control switch and release switch (although my wiring diagram shows it as 2 things).

I had assumed that the wiring diagram would be very similar for 89 and I was wrong. It would be best to get a diagram for 89 to trouble shoot your problem.

Perhaps someone on here has it or you could pay for it at www.alldatadiy.com

Sorry I was not much help on this one.

//2000CAYukon

Got it fixed......I took a jumper wire from the Lt. Green wire to the Brown wire on the cruise release switch. It works just as it should.