[Toro]

It's a pass through. Ground either of them. When the lock engages, the ground will appear on the other. Wire this up to a relay and a light on the dash of some type. The light will indicate when the lock is engaged.

Spst relay

85- 12v fused (low amperage)
86- ground from diff
30- 12v fused(whatever the lightneeds)
87a- to + terminal on light

Light
+ From pin 87a on relay
- Ground

There are probably 4 or 5 different ways to do this. Opinions may vary.