The reverse switch circuit is powered thru the ECU-IG 7.5 amp fuse in the engine bay when the ignition is on, so check fuse.
You would have to remove the intake assy to access the switch on the trans, and you may be able to test it with a multimeter without taking it out if you remove the plug, and select reverse.
Otherwise unscrew it and test by pushing in the ball on the end.