My 85 Ram had cruise control but someone removed it.
I thought it would be simple to reinstall it and found all the parts I needed at a couple different junk yards on a 88 dakota(servo, speedometer cable from servo to trans). The wiring was cut from the brake switch and had to buy a new one from the parts store. I found a throttle cable and spedometer cable from speedo to servo on an 86 Ramcharger. Got everything hooked up and found out the wires in the turn signal stalk were cut off in the column.
Luckily the Ramcharger had one.
Still cannot get it working. The servo will only engage when the resume button is held down.
Checked the wiring and switch operation and everything seems fine.
I can even hear a clicking noise from the servo unit when I hit the buttons. The unit just doesn't set speed.

 

do you got everything hooked up properly and the servo has vacuum line running to it? also does the air bag in the servo move like it should?

 

Everything is hooked up, even the vacum line.
It does come on and hold speed with the resume button held down but will not set and stay.
I hooked it up according to these diagrams and checked the switch operation and it was fine.

 

After a closer look at the wiring diagram I noticed the white and yellow wires on my plug under the hood were reversed from the picture(Download.jpg).
I reversed the wires and it seems to work perfectly. The only factory wiring used was the 3 wires through the firewall.
Downlaoded that from ramchargercentral.net. Strange that chrysler corp would change wiring colors from such similer vehicles.