In run 257 Backshop Letters, questioner Gary asked if there is a way to add backup lights to his 681 turbine. However I believe Jim's answer may be in error.
The mechanical reverse unit drum has embedded copper pieces that make contact with stationary fingers, that in turn connect to a grounded motor field coil, and two isolated armature brush plate connections. In neutral position, the two middle 'C' shaped fingers rest on plastic, no current flows, motor off. In the other two positions the embedded pieces make connections such that the field is energized and armature is connected so motor runs forward. In other position, the armature connections are reversed relative to field winding causing the motor to run in reverse. Thus there is no separate reverse unit contact or isolated connection that is exclusive to backup function that would light the lamp(s).
My reference is numerous reverse unit schematics shown in Greenbergs Repair and Operating Manual. I believe Gary's 681 probably follows the same scheme. Other answers welcomed.
