Hello all. I have a 90 740 with the bosch system non turbo. The cruise control will not engage at all. I have checked for power from the blue and red wire that is fine, checked to make sure the brake switches are working, they are. The black and white wire has small amount of voltage, under .8v. The switches on the column are working as well. I removed the cluster to check if there is sensor voltage and that is 7.52 volts at 30 mph. Checked the vacuum servo and that is working as well. I have a 87 turbo and I have been checking the parts from the 90 to the 87. I am stumped! Anybody have any ideas where to go now? The only differance so far I have seen is the sensor voltage from 87 is lower at 5.62 volts. I also noticed that the orange signal wire stays at 12v and does not go to zero when the cruise is engaged. I looked into FAQ for wire diagram but did not find what I needed. Did I miss somthing? Thanks, Pauli

I had this problem as well. At first, it was the 90 degree rubber fitting that is on the servo. When looking at it, no problem. but when I bent the rubber fitting in removing it, I could see it was split enough to kill the vacuum. Then I did the lifting of the brake pedal, to see if the cruise would work and it did. As soon as I removed my foot from beneath the pedal, the cruise cut out. Simple adjustment of the brake pedal valve, and now I have cruise again.
just a thought.

Have you checked to make sure the relay controller under the dash is connected? It's on the firewall, I can maybe find the part number for you if you need.

I found at one point that something I did under the dash knocked the connector loose, and knocked out my cruise control - fixing it was that easy.

Did you check the diaphragm and the vacuum tubing to the brake switches? Also, did you check which nipple the tube is on?

Hope that helps,
-Will
--
1990 740 Turbo, on its way to stock specs, maybe beyond

Thanks, I wish it was that easy. Pauli