If post 17 does not fix it, get right down to the starter and remove the small wire from the small terminal. Now "rig" another wire to that terminal long enough you can jumper it to the battery "up top." If the problem still happens, it HAS to be in the starter or alignment problems.
WANDERING: The ignition switch has two contacts that are hot during "start." One is the normall brown IGN2 which bypasses the ballast resistor and feeds the ignition system hot battery power during "start."
The second is the yellow start wire which fires the starter relay. If someone had problems, etc, may have interconnected those wires OR IF THERE is a problem in the ignition switch, that circuit can cause a 'backfeed' The yellow should be DEAD in the run position of the key.