I have just acquired a 1995 c1500 pickup.Pretty clean, but the break light is stuck on. I have checked the parking break switch. I got a GM code reader, and get a code 73. "4WAL control unit fault" On my truck the ABS light is not on, just the break light. When I use the code reader, the break light flashes, not the ABS light. Is this something else, or is my ABS system bad? FYI, I have changed the master cylinder, and bled the breaks,(nasty) but clean now. The breaks work.