I think I've read most of the write-ups on diagnosing cruise control issues, but don't find any info on testing the switch (blinker) or the pump motor (near the brake booster under the hood).

I've fixed a brake light issue but that didnt restore cruise. checked the brake pedal switches (visually), checked fuses, etc.

and still nothing.

 

Have your instrument cluster been removed recently? There should be a yellow wire coming off the double male spade on the back of the cluster. This wire provides the speed signal to the cruise control module. Make sure that this wire is attached. Also, you may want to check your engine codes. If you have a 3-1-1 code (missing speed signal) then the cruise control won't work.

 

i'll check the wires.

no codes are showing

 

First things to check are your vacuum lines, diaphragm, etc. The stalk switch is often sticky too, if not used regularly.
"Checking", make sure you indeed are eliminating possible issues. How did you check the brake switch, i.e?

 

the cruise on our 87 240, the vacuum activator down by the gas pedal, its metal cable was completely corroded

 

by checked, I meant, checked the adjustment, made sure the vacuum lines werent broken or disconnected, made sure the electrical connection was connected....

I pulled the instrument cluster just now and found only a Red/White wire unhooked. no yellow to speak of. I connected the R/WH to the double male lug but still no change.

 

my original question was aimed at that: how do I actually test the things that are often mentioned to check....

 

AAHHH, disconnect that red/white wire immediately, unless you have a tachometer!!!

thats direct from the coil, and will FRY the speedo or whatever it is you connected it to

 

The brake switch, if you have brake lights is fine.. Make sure that the Vacuum Dump Switch below the brake switch closes/opens. Autos have one of those, manuals have two. Both have to be closed, holding vacuum pressure... Release pressure when pedal(s) are pressed.

The other two major parts, the CC module and the vacuum pump, rarely go bad but not never. Don't know actual testing procedure for those, I just swap them with "known good" ones to test them.

 

best way to check switches is with a digital multimeter in 'ohms' mode, unplug the switch, and connect the meter across the switch connectors.

I do believe I'd unplug the vacuum pump and use some clipleads to jumper power to it and verify that it can in fact move the bellows that moves the gas pedal. the vacuum pump has three wires, power goes to pin 3 (yellow red wire), and then you ground either pin 2 (green-yellow) to suck air in and go faster, or pin 1 (orange) to release the vacuum, and let the pedal back up. if /that/ works, then your problem is going to be in the control switch cluster, or the cruise control unit.

 

That red/white wire is a killer unless you have a tach. I spent two years replacing pieces of the cruise control on my 90. Turns out I had connected the R/W wire at some point to the instrument panel. I ended up buying a new instrument panel before I got it fixed.

 

yeah, the red-white wire comes directly from the coil, so its got quite a bit of pookah on it.