[90 suburban]

Hello, NEED HELP

Cruise worked intermit last week and now not at all.
Have replaced transmission speed sensor, brake light switch, cruise switch stalk.
Verified fuses are good.

Checked for voltage at the connector for the cruise ...
Key switch on...
1. red wire showing 12 volts
2. blue wire shows 12 volts when r/a pressed
3. green wire shows 12 volts when set button pressed
4. gray wire shows 12 volts continuous ...

I believe the gray wire should only have 12 volts when brake applied... since it is showing 12 volts all the time the cruise control thinks the brake is pressed.

Could it be a short in the column?

 

[90 suburban]

Vehicle is a 1990 chevy suburban. R1500 5.7 gas 2 wheel drive

 

[Crawdaddy]

The factory cruise also has a vacuum switch attached to the brake pedal to signal cruise to disengage. Have you checked it? I occasionally have issues with my suburban where I have to hit the brakes a couple times or pull up on the pedal with my foot.

Do you feel the cruise attempt to engage at all?

 

[90 suburban]

Thanks for the bounce back Crawd..
I did check the cruise vac/switch also... 12 volts present when brake pedal pressed.
About a year ago I had the turn signal multiswitch and cruise stalk replaced at a steering column shop. I had the tech use the new stalk I had already replaced in the column and after installing realized I had broken the R/A wire on the connector. Mostly worked to set the cruise but the r/a function didn't work. As I mentioned the cruise has intermittently worked but quit altogether last week. Doesn't attempt to engage at all.
Mechanic buddy printed out a diagnostic procedure for me... It states the gray wire of the connector where the blade plugs in would have 12 volts when brake pedal pressed. It has 12 volts all the time. Seems that would be the problem but I don't know how to remedy.

 

[Crawdaddy]

If you've diagnosed power on a wire that shouldn't have constant power, my first step would be to move up to the next switched device up the chain. (Presumably the brake switch) Test for power there. Wiring can be a little intimidating because there's so many wires, but most electrical circuits in the square bodies are really pretty simple.

The wiring harness for the cruise comes into the truck by the main bulkhead connector on the drivers side. It's lower and closer to the wheel well and a bit closer to the engine than the main harness. It'll be wrapped in tape with a vacuum line. Inside the cab, it's pretty close to the floor and then heads up around the column to pick up the brake light switch, vacuum switch, and other column wiring and its main power feed.

 

[90 suburban]

Thought I would share how I fixed my cruise in 1990 Suburban.
None of the parts houses or rebuilders offer the vacuum cruise servo for 90/91 models.
After trying for days searching the internet for a replacement I decided had nothing to lose in disassembling the servo to see if something was broke.
Using a voltmeter discovered that one of the coils contact points didn't have continuity. Probed the wire wrap and found a spot where the wire was broken...peeled off about two feet of wire and found the other end of the wire. Checked continuity of these two loose ends and had a reading. Peeled a wrap or two from both ends, stripped the coating, twisted together and coated the twist with silicon adhesive. Had continuity now at that spool's contact points so reassembled the servo and test drove. The cruise engaged but at highway speeds was loosing speed. Fix was to remove the redundant brake vacuum line from the servo and capped the fitting. I Have know driven over 500 miles with a fully functioning cruise. Happy day!