Nuetral Safety

You may have TWO problems
1 As mentioned above you may have a clutch switch, already addressed above

2 Seat belt interlock


So far as the interlock, THIS part of the equation is in series with the yellow start signal coming from the key. Look for a relay box under the hood with a reset button. That relay should have two large yellow or yellow/ tracer wires. Connect them together.

In other words you twist the key, but the interlock must be "made" to apply power on through to the start relay BUT the start relay has no ground because the clutch switch is not depressed, so you ground that wire to allow the start relay to finally fire.