Cruise Control

No. Just the "cruise" light comes on.

Is there an indicator light that normally comes on? What does it indicate during fail?

i discovered that if the mechanic doesn't snap the switch wire parts together securely, putting on your brakes does not turn off the cruise control.
produces an anxious moment or two.
bumpy

Several ideas.. One is the brake pedal/light switch. If any of the following conditions exist the cruise will not work.

1: Speed too slow (Not sure what the cut off is, 20 mph it won't work)
2: Foot on brake pedal
3: Brake light switch stuck ON
4: Brake lights burned out
5: Brake light fuse blown
6: Bad speed sensor. (Should affect speedometer).

and then there are computer and control issues, bad parts and so on. On Drive by wire motors like the modern 8.1L ... there are fewer parts unique to the Cruise.

MOST common causes of Cruise malfunctionb are brake pedal/switch related.

Make sure your brake lights are working properly, an improperly adjusted brake light switch can prevent proper operation.
Check for vacuum leaks as well.

I had a similar issue recently. At the same time, my brake lights would stay on from time to time. Turned out the brake pedal was not always returning fully and this caused the brake light to stay on and the cruise to think the brakes were being applied and thus not engaging.

If it's a mechanical cruise as many GM models are, it's likely a vacuum issue. If you have an electronic cruise there are a number of possibilities from speed sensor, switch, control board etc.

when this happened on my Ford chassis the VSS? wasn't working right. a $9.00 part at the time.
bumpy