I have a 1993 LeSabre Custom, and the cruise control has been
inoperative for awhile. If I try to enable it (move ON/OFF switch to
ON and press SET), it may kick in for few seconds and then quit, but
most of the time the cruise light simply flashes once and then stays
off when I press the Set button.

At the connectors to the Powertrain Control Module (PCM) I have verified the following:

To check the CC switches on the lever, I checked
12 volt on pin D2 of C3 (the green connector) when the ON/OFF switch set to ON.
12 volt on pin D3 of C3 when SET button pushed (and ON)
12 volt on pin D4 of C3 when Resume pushed.

To check the brake switches, I checked
12 volt on pin D10 of C1 (large black connector) when ON/OFF in ON, that goes away when brake pedal is depressed.
12 volt on pin A5 of C2 (smaller black connector) that goes away when brake pedal depressed.

(Note:
All the above voltages were OK. When I checked them, I wiggled, shook,
etc the CC lever and brake pedal to try to get a failure but couldn't)

Checked
continuity of wiring between PCM connectors and the connector for the
cruise control servo, and between the PCM and the Vehicle Speed Sensor
(VSS). VSS seems to be working - I unplugged it and got Check Engine
Light and no speedometer.

Checked all vacuum hoses. Even set up
a test where I applied voltage to operate the vacuum solenoid and vent
solenoid in the CC servo. The servo caused the engine to accelerate
perfectly, which should indicate that vacuums were there and functional.

I
can't think of anything else to test. Maybe the PCM itself is faulty,
but I don't know how to tell. Anyone have any ideas of additional
things I could try. Thanks.

Update: As of 6/2/08, it may be fixed. Yesterday was rainy and humid and the cruise worked about 75% of the time. Thought it might be a connection problem that the humidity affected, so I got some emory cloth and contact cleaner and went to work on the following:
- connector for the C/C in the lever on the steering column
- connector to the C/C servo
- connector to the VSS
- 3 connectors to the PCM.

Today I drove it quite a ways and used the C/C as often as I could - worked every time. Hopefully that was all it was and won't come back.

Edited by: GatorInAtlanta