The neg connector goes back to the ecu , Pin 21 [ blk] for coil T/3 [ plug 1/6]
T1 is pin 8 , T2 is pin 9.
You may have a bad connection there .
You have the early FM system and the ecu was changed for the 94/95 versions . I remember seeing a service sheet here somewhere that stated these had a problem was switching transistor heat sink dis-connect for 1 and 6 circuit.
Let me see if I can find that and I will get up schematic
This may also show up on pin #8 of diagnostic socket as a code 21 for T3 output.
Simple led tool will get that info..