Could pull the ABS codes
ABS Codes:
Shorting pin "H" to pin "A" on the ALDL connector will cause the ABS light to flash ABS codes.
terminal H is next to G in the pic ( pre '90 shown )

Could pull the ABS codesThe 2nd is the service ABS light coming on. The vehicle rolls the required distance but the hydraulic assist does not kick in.
Sounds more like a intermittent power / ground problemThe ABS light comes on, the dash lights will flicker continuously and the engine runs rough.