83convertible1001

I just came across this solution to the problem of the Cruise Control not working on my 83 Mustang and I hope this information will help others

This is for anyone with an older Mustang, or any Ford vehicle, fitted with a Cruise Control that uses a Vacuum Servo Throttle Actuator and would like to get it functioning again.

Might I suggest that after verifying that no fuses are blown, your brake lights are not blown and before tearing the car apart or contorting yourself into a pretzel to check wiring & connections, that the Vacuum Dump Valve mounted next to the brake light peddle switch be checked. If this valve is leaking because it has gone out of adjustment or a failed seal the cruise control not work. The valve is held closed by the brake peddle and will open dumping the vacuum on the servo when the brake peddle is depressed. This particular valve has a history on some of the later models and the conversion to electronic servos in the mid to late 80's of becoming loose in its spring retainer and going out of adjustment over time.

This is a quick and easy way to verify the valve is holding vacuum without removing the valve from under the dash. This can be done at an easily accessible point under the hood by doing the following test using simple tools such as a syringe, a vacuum pump of some kind (hand or electrical), or even a turkey baster to create a vacuum on the line between the servo and the valve.

1: Trace the dump valve vacuum line to the point where the line goes through the firewall from the servo. Remove the vacuum line from the servo
2: Insert the end of the syringe in the vacuum line with the plunger fully inserted into the tube and attempt to pull the plunger out. If the plunger moves out easily the valve is leaking. If a vacuum pump is used air will be heard leaking under the dash. If using a turkey baster the suction bulb will expand as air is drawn in or remain compressed if tight. Do not use compressed air to test the valve as it could damage the seals within the valve

If the valve is leaking it may be possible to reseal the valve by adjusting the position of the valve with following steps
1: Reach up under the dash to find the valve and wiggle it while pushing the valve toward the brake peddle. You will hear an audible click as the adjustment ring on the valve passes through the spring retainer clip
2: Check the line again with the syringe or whatever method you are using to put a vacuum on the line to see if there is more resistance
3: Continue to adjust the valve 1 or 2 notches at a time and check the line for vacuum until you can no longer pull out the plunger of the syringe or the pump and or baster indicates the line holds a vacuum. If after doing doing 3 or 4 valve adjustments and the valve stem that contacts the peddle is compressed at least 1/2 it's travel, the valve still doesn't hold a vacuum, the valve has probably failed and needs to be replaced.
4: Reconnect to the vacuum line to the servo and go for a drive to test the cruise control.

If the vacuum test proves the valve holds a good vacuum and the cruise still does not work. You are stuck with either contorting yourself or hiring someone to contort themselves to go under the dash to find the bad connection or switch