Hello all,
For what it is worth I'll let you know what happened. A few years ago I installed 4 blink then constant on LED brake light bulbs in my '04. They worked perfectly. A few months ago I started having issues with my cruise control. Whenever the headlights came on automatically or I turned them on manually the cruise would not function. Daytime running lights had no bearing on the problem. The cruise switch on the steering wheel would illuminate but the cruise indicator on the cluster would not and the cruise function would not operate. Also the ABS and Traction control lights would come on in the cluster. I pulled the codes. C1295 Brake lamp switch circuit open, C1238 Brake thermal Model exceeded, C1236 low system supply voltage. On a hunch, I swapped out the LED brake light bulbs and replaced them with halogen 3057's. Problem immediately disappeared. All codes vanished. Cruise function restored and no traction or ABS lights. I do not pretend to understand what happened or why the LED's worked for so long then the system decided to act up. I'm an old mechanic who turned wrenches for 45 years. Not an electrician.

 

Interesting find. I have seen something sorta similar.
- In my 2004 Monte, I have aftermarket LED tail lights (they come built in with a solution to stop hyper flashing). And I wanted the aftermarket LED 3rd brake light. If I used BOTH of those aftermarket items at the same time, traction control/abs had an issue and I got some code starting with a C (I think it may have talked about a ground to the wheel speed sensors, but I am not 100% sure). My father gutted a factory LED 3rd brake light to mod the components to fit my aftermarket 3rd brake light, problem solved.
- A friend with a 1994 Firebird had his incandescent 3rd brake light bulbs go out. We put LED replacements in. He had the same problems I just mentioned. Swap to incandescent again and no issue.

GM has done something that I too don't understand with the wiring for these systems.