Think I found the Answer ???... any confirmations....
737 DISPATCH DEVIATIONS PROCEDURES GUIDE -
"the -300/-400/-500 the N2 tachometer generator for the number 1 engine must operate normally for dispatch because it provides a signal to the landing gear transfer valve to identify when the number 1 engine has lost power. Verification that the N2 tachometer generator is operating normally
(when N2 tachometer indicator is inoperative) can be done by; (1) checking the AVM Analyzer (M1240) for corresponding fault code regarding N2 Tach signal loss or (2) observing that the engine start switch automatically moves to OFF during the engine start. If the number 1 engine tachometer generator is inoperative, it must be replaced or switched with an operative tachometer generator prior to dispatch."