Brake light and ABS system light on

[06 Southern comfort]

Brake light and ABS system light on.
After purchasing 06 Z71 that have been stored for five years. The brakes had hardened and was sticking calipers the rear were no good. After replacing both rear calipers and new brake pads front and back. The ABS and brake light came on with a warning to fix the brake system. After a lot of research( with a Scan tool ), checking all grounds ,checking speed sensors ,bleeding the brakes for the third times and the master cylinder and proportioning valve. I stumbled across the fact when I unplug the brake sensor on the proportioning valve the light will go off. After more testing I determine the switch was bad it was stuck in the clothes position. This brake light switch is normally open. The dealer wanted $40 for the switch. I ran to a local salvage yard picked one up for $2 dollars fix the issue.
I hope this information helps someone that may run into hey similar situation.

 

[Raekal]

I guess just to add onto the helpful info here for the google searchers. We recently found out that the random cause for the ABS + brake light coming on my 2001 tahoe was due to bad front wheel bearings screwing with the wheel speed sensors. Some days it would come on, others it wouldn't. The only notable causation I could think of is that it was more likely to happen during a hard turn. Which makes sense, seeing as the wheel hubs could separate if they were loose.