Check For VBAT To ICM
WARNING: This page is about a different car, the 1994 Mazda B3000 and 1994 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.
Turn key off and disconnect PCM. Set DVOM to 20-volt scale. Turn ignition on. Measure voltage between breakout box pins No. (+) J51 (VBAT E) and (-) J7 (BAT negative). If voltage is greater than 10.5 volts, go to CHECK FOR GROUND OPEN TO ICM. If voltage is 10.5 volts or less, repair open or short in circuit from ignition switch.