I have gone though several dash clusters on my 86 C4 and now my cruise control system will not work. Could it be the latest cluster keeping it from working. I don't know what year in was from. Is there a way to test that system? Did all C4's come with Cruise Control?

 

So the problem happens with the new cluster installed?

If not I would check the vacuum line going to the cruise control module above the battery. I found an open vacuum line on my 86 and splicing that back together fixed mine.

 

The cruise was working before the last replacement and I had it checked out and was told I was not getting power to the switch so I replaced the switch and that did not work, so now I am wondering if the cluster is setup for cruise control.
Thanks for your speedy reply.

 

This from the 1986 FSM:

CIRCUIT OPERATION
The Cruise Control System operates a
mechanical linkage to the throttle by means of
a vacuum motor. This is a diaphragm moved
by a vacuum applied to one side. A solenoid
operated valve connects the vacuum motor to
a vacuum tank. Another solenoid valve vents
the vacuum to reduce suction. The INSTRUMENT
PANEL controls the vacuum motor
and the throttle by pulsing these solenoid
valves on and off.
One input to the INSTRUMENT PANEL is
the vehicle speed. This input comes from the
Vehicle Speed Sensor. If the actual speed signal
is different from the speed that was set into
and remembered by the Instrument Panel, the
Instrument Panel generates pulses to change
the vacuum and return the vehicle to the set
speed. The Vehicle Speed Sensor is mounted on
the transmission. Other inputs to the
INSTRUMENT PANEL are from the
"Cruise" Switch and the "Set" switch. A disengage
input to the INSTRUMENT PANEL
comes from a switch on the brake pedal. In
cars with a manual transmission, a switch on
the clutch pedal will also disengage the Cruise
Control.
The two outputs of the INSTRUMENT
PANEL operate the coils of the vacuum valve
and the vent valve. Both valves are located in
the Cruise Control Servo. These valves move
the throttle by means of the vacuum motor.
The Servo Position Sensor coil senses the position
and motion of the vacuum motor. It feeds
this information back to the INSTRUMENT
PANEL to provide smooth acceleration while
the vehicle is in Cruise Control.

 

Not all!!!!

I believe if you had a 'correct' FSM you could confirm cluster pin-out population to determine if your current cluster is a correct or NOT!! If you don't have an FSM I'm quite sure Bryan (batee.com) has correct pin-out for clusters.