Cruise Control diagnosing

[PeaveyBassist]

So my cruise control used to work and one day it just decided to...stop... I finally decided to work on fixing it tonight so I went out to the car to inspect a couple things. I went to the control unit first since it is the easiest to get to. (Above the ECU above the glove box, Fuse 6 is GOOD) Pin 1 has 12v with the key on RUN. Pin 9 has a good ground as well. I checked continuity between the blue/green wire and 12v when you push the switch to accel/set and it has continuity when pushed. My next step tomorrow morning will be to check that the switch has no shorts in it. Then check the clutch switch. Then see if the control unit is getting a signal from the gauge cluster. When I check for the speed signal at the connector for the control unit, I'll be using the blue/ylw wire. Do I need to be checking for a resistance or voltage? I already pulled the control unit out of it's case and nothing is obviously blown up. Anything else I can check without replacing stuff with "known good parts" ?

Will

EDIT: Car is a 1990 325is. manual.

[StereoInstaller1]

I got nothing for ya, but my wifes' car has the same story...but no time for fixing it yet.

Gonna start with the 2 pedal switches in this case though.

[Red88]

Yeah, definitely check the pedal switches. Pull the pedals up with your feet to see if that closes the switch. Mine did and I wrapped up electrical tape around my pedals to make the switches close all the way.

[PeaveyBassist]

Clutch pedal works properly. It is open when the pedal is up, and closed when you barely push the pedal. For some reason, when I went to drive, I had no brake lights and the brake light switch is open no matter what. BUT they have been working when the cruise has not. Also, at rest the switch should be open so that shouldnt affect the cruise working. Checked the speed signal and it is properly going to the cruise control unit. Use pin 6 (blu/ylw wire) and a ground and check for voltage. The clutch pedal makes the signal open. When the clutch is up, the voltage should be 5v at rest. I got 4.25v at 30mph and 3.88v at 35mph. About 3.25 at 50mph so the control unit should be receiving the speed signal from the cluster. I found the connector that goes from the control unit to the servo motor under the dash by the clutch pedal. It is up against the firewall towards the bottom right by the grommet. About 7 pins in a small round black connector. My next step will be to try and pin that connector to see if the control unit sends a signal to the servo motor when you hit the accel/set switch above 30mph. If I cant get a good reading, I will replace the control unit and see what happens. If that doesnt work, I would assume that it is the servo motor that is the problem. Hopefully this thread will help someone else diagnose their cruise control problems!

[PeaveyBassist]

Well... had the control unit unplugged for about 1-2 days. Tried it yesterday and it didnt work. Tried tonight on the way home from work, and cruise control set and worked 100% fine. Talk about weird. Maybe a bad connection on the plug at the control unit. Who knows!