I haven't looked at the schematic, but I think the tach signal is what the ECU looks for to keep the fuel pump in operation when the key switch is in the "RUN" position.

As previously suggested, if all of the electrical functions are not connected, the engine may not run.

The idea to check the fusible links near the battery is good - also, the square plastic main fuses at the battery can be easily checked.

Frank

'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum