To test the electric component of the shift switch, you'll need access to the ignition and forward and reverse terminals.
The original wires are color coded which will make identifying each one easier. To test the switch for the forward position,
connect test lead of a multimeter (set at continuity) to the ignition lead (purple or red), and the other to the forward lead
(green). Next, move the shifter lever though the forward, neutral and reverse positions. The meter should only show continuity
when in the forward position. To test for reverse, move the shift lever into reverse and connect the test lead of the multimeter
to the ignition (purple or red), and also to the reverse lead (blue). Again, move the shift lever through forward-neutral-reverse.
The continuity should only show on when the lever is moved into reverse. If you don't have continuity as shown above, your
switch is defective and needs to be replaced.