Hey all - trying to diagnose an inop cruise control system. System is totally dead - no clicks or anything.

original stalk was showing high resistance through the set switch, so I replaced it with a new Standard stalk. Still does not work.
Clutch switch was showing high resistance even with the button pressed, so I opened the switch up and cleaned the contacts. Now it has good connectivity. Still does not work.
Brake switch seemed OK, but i cleaned it anyway. Still no dice.
I swapped the cruise servo for one from another GM model - no difference.

My question is - what clutch switch does what, and what brake switch does what?

The clutch switch in question only has one 2-prong connector running to it, but it actually has two 2-prong plugs. one of the plugs is disconnected. Is this normal?

One brake switch has two 2-prong plugs that are both populated. The other brake switch is like the clutch switch, and has two 2-prong plugs but only one is populated. Is this normal?

I still have to check the vacuum canister and dump valve but the car is rust free, so I doubt the can is rusted out.

Thanks all -

[This message has been edited by masospaghetti (edited 12-05-2010).]

Are both the clutch and brake switches adjusted so they are fully depressed when the pedal is at the rest/full up position? They are designed to shut the cruise off when either pedal is depressed.

When you operate the slide switch on the stalk the little solinoid above the juice can should click.

What year is your car? I'm not sure about the 88/87 but earlier years had a small electronic control box under the carpet on the tunnel right about the driver's right knee.

I'll see if the solenoid clicks, I'm pretty sure it doesn't.

I've adjusted the pedal switches so they are depressed when the pedals are up, I just wanted to verify that there are connectors on the switches that have nothing going to them...and also to verify which brake switch did what (I assume one is for the brake lights, one is for the cruise function).

Thanks!

One brake pedal switch should have an orange, white, and one or two light blue wires going to it depending whether you have the high mounted stop light or not. Both connectors for that switch are used for the brake lights. Both halves are normally open, that is, the orange terminal is not connected to the other two or three wires with the pedal in the up position.

The other brake switch should have a grey wire and either a dark green (manual), or brown/white (auto) going to it. That switch is for the cruise control. It also has one empty socket with two prongs. Both sides of the switch (the used side and unused side) are normally closed. That means with the pedal in the up position, the grey and the green wires are electrically connected to each other until you press the pedal.

On the clutch pedal, there should be a dark green and a brown/white wire running to one of two sockets. The other socket is left empty. This switch is also a normally closed switch.

This is getting ridiculous.

I've changed the signal stalk, cleaned the brake and clutch switches, added a ground to the cruise servo, fixed my vacuum can, and performed most of the tests in the troubleshooting manual....seems I might have a defective module. I can't believe how many parts tested bad, and how the system still doesn't work. The vacuum can, FWIW, looked fine but was riddled with cracks. Now there is vacuum all the way to the servo.

The dump valve does click when the brake is pressed.

I've tried two solenoids - the original one, and a salvaged one from another GM vehicle that looks similar but physically a little bit smaller - no difference.

Where is the best place to get a spare module?

found it

[This message has been edited by red85gt (edited 06-08-2011).]

Did you check the coil inside the cruise module in the engine bay? This is exposed to the elements and could be the problem.

When you checked the switches, did you just check for resistance or voltage?

[edit]

There is no need to swap any parts until you do the following checks (I am working from the wiring diagram):

Ok, measuring voltages on the cruise module (the one under the carpet near the gas pedal):

Pin A should have +12v when the stalk switch is on. If not you will have to check if you have power going into the switch, if not you need to check back to the fuse box – if you do, then there is something wrong with the switch/wiring.
Pin G should have +12v - in not, check your brake and clutch pedal switches again.
Pin L should have +12v when you press the 'Set' button.
Pin M should have +12v when you press the 'Resume' button.

If good, then your switches are all working – if then you have a problem in this area.

Then check if you have +12v on the vacuum release solenoid in the back (should be a purple wire) - you may also want to check that it has a good ground on the other side of the coil.

Again check the coil/solenoid in the servo module in back and make sure it is working correctly and free to move. The cover IIRC has just a couple of screws holding it on - but you will probably have to remove the unit from the car to remove the cover.

You can also verify the vacuum and vent valves on this module by supplying power pins E and A respectively are opening and closing.

If you have a vacuum gage/pump, you can check if your lines are good – disconnect the line near the dog bone and pump it down and see if it holds vacuum (this assumes your line is good on the motor as well).

If this all checks out, then you possibly have a bad module, the rest of wires are hard to check without the car in motion and a scope.

[This message has been edited by Mickey_Moose (edited 06-08-2011).]