This may be a long one but I’ll give as much info as I can. Truck is a 1993 (build date 6/93 according to door tag) K1500 originally with A/T. Swapped in a good and good running 5.7L and NV 3500 from a 1988 K1500. Engine occasionally won’t start and when that happens injectors are not spraying fuel, fuel pump relay also makes a god awful noise when this happens. Replaced ignition module in distributor as well as fuel pump relay. Problem persists intermittently. Also pulled the ignition switch from above the steering column hoping it was a bad connection or box. Jumping the wires in the plug makes no difference. Tried hooking scanner to it MTG2500 tells me to connect GM1 connector to ALDL port and turn key on then tells me unable to connect so can’t verify any sensors are working. Thinking I may need a different connector for the scanner. When the injectors do spray the pump relay makes no noise and the truck fires right up and idles good some sputtering when you rev it up and it backfires a little bit. Any thoughts on this issue or ALDL connection are appreciated.