pull the yellow wire off of the starter relay to disable the starter then with a helper: with key "on" and held to "start" the coil positive primary terminal and the blue/yellow ECU terminal need to be hot (2 key positions/2 terminals= 4 checks) (plus the red/green ECU terminal if an OE 5 pin ECU (OE 5 pin ECU has a functioning 5th pin that is fed by the red/green wire). I'd seperate/clean the bulkhead first