Triumph Repair: Reverse lamp switch, shift mechanism, bell housing

Question
Howard--my reverse lights don't work on my '72 Spitfire.  I have the engine and transmission out and see 2 switches on the transmission housing.  From the color of the wires (one green, one green/brown)it appears the reverse switch is under the back cover of the shift mechanism.  
What is the other switch that sits on top in a bracket just behind the bell housing?  It looks just like the the other switch but has 2 green wires to it.

Answer
Hi Dan,

When you have extra switches on the gearbox, that is an indication you have an overdrive unit. The extra switches prevent the car from being shifted into overdrive in any gear except 3rd and 4th gear. If you were to engage reverse with the overdrive engaged it will destroy the overdrive.

Howard