The next thing would be to switch instrument panels. If you have a friend with a LX or LS machine I would take my board and attach their harness connectors to the panel and see if their machine acts the same way. You can also attach their panel to you machine's harness connectors...................You can also check for continuity between the wire connector of the fuel shut off solenoid and pin 5, ltblue/o, of the instrument panel larger connector..........Check for power at the instrument panel. With the key off you should have power at pin 4 when you sit in the seat, pin 11 when you fasten the seat belt, and pin 14 at all times...........Turn the key on and should now have power at pin 12 also...........Now turn the key to start and you should have power at 10............It is also possible the fuel shut off solenoid is drawing more current than the instrument panel can safely supply. During starting. and when the service run switch is in the service position, current is supplied to the fuel shut off solenoid from other sources and not the instrument panel.
