She's a '90 and using an '88 service manual but can't find a cause.
Dash unit lighting up but cannot get it to engage? Any ideas folks?

 

Something similar happened to my FD when I first bought it. The cruise light would come on and the car tries to stay on the gas to keep the speed but fails and the light turns off.

I pulled the fuses under the dash to inspect everyone one of them. None of them were burnt so I put each one back. I guess there was a electrical contact problem and somehow the fuse pulls solve the problem.

Give that a shot!

 

Pull the switch out of the console and take it to an electronics repair shop. Try to find a small, local one where they'll do it in front of you. If the cause is because of a burnt-out whatever, they'll find it right there and you'll be back out the door in about a half hour. If not, at least you'll know it's 100%.
I pulled all the circuit boards out of my FC when I 1st got her and almost every board had cold solder points that had cracked. I took them to a little place that also does water purification and dry cleaning. Anyway, the point of that is that the guy does all his electrical work at a desk right behind the counter. I walked in, I walked out, it was all good.

Also, get the vac lines checked. Can't hurt.

ttyl,
Amur_

 

I vote with Amur. If it is operated by a vacuum, get under the hood on the passenger side(right side) and check out the vacuum hose going to the actuator. If thats good, and it has been working recently, follow the cable to the throttle body and see if the cable is still attached to the throttle. And I don't mean attached to the bracket on the throttle body, I mean there is a keeper on the end of the cable that looks like a minature barrel on the end of the cable that fits in a groove in the throttle crank. Don't poo poo that thought. Had it happen to me. Fixed it in good ole shade tree style. Made a mold in a piece of wood similar to the barrel, poured some JBWELD in the depression and inserted the end of the cable. Shaped to fit when it set up. In use a little over a year later. Time Bomb waiting to go off when I'm the appropriate distance from home. Preferably at night, cold and raining. Cheapskate here. If those two are not it, write back. Other ideas available if you have a digital voltmeter. If you have an all electric actuator, disregard the part about the vac hose.

 

If its a 90 gxl its vacuum actuated. Ive done some cruise work before, including transplants into non-cruise cars.

First thing, I assume the MAIN light comes on.

I assume youre using the stock cruise ecu and switch and actuator for this car.

When you get up to speed, and hold the set button in, does the CRUISE light come on the switch?

IF so, then your problem is in the actuator. See if it is plugged in, or might not be working at all.

IF not, you have a problem with the switch, cruise ecu, or inputs to it, which include the sped sensor in the instrument cluster(ifyour speedo work this most likely works), the brake pedal switch, and the clutch pedal switch.

The 89-91 cruise systems have a self-diagnostic function as described in the FSM.

TO begin, turn on the ignition switch, but dont start the car.
Next hit the MAIN button.
Hole the arm UP for 3+ seconds then release. The CRUISE light should come on for 3 seconds then go off. The cruise will flash the error codes, so note what they are. They repeat every 4 seconds.
Push MAIN to deactivate.

When I installed cruise on my 89 gtu, it would light MAIN but not cruise and would not engage. Later I tracked it down to the fact that my gtu did not have the proper switch on the brake pedal for the cruise control to read off of as well. I swapped this part and all was well.

IF you need a scan of the FSM pages concerned let me know. hypntyz@charter.net

 

Thanks a bunch folks. Will get to it this weekend.

 

I had a simmilar problem in my 88.. Turns out there's some switch on the brake pedal (mm..mabye clutch.. one of the two) that gets pressed when the pedal is fully released, and it wasn't getting fully pressed. I taped a penny to it to give it a lil extra travel, and that fixed it.

I like 0.01$ repair jobs..

-Tesla