[pjmoreland]

The switch should have four prongs on it. Two are for the back up lights and two are for the neutral safety connector, which doesn't allow you to start your truck if you aren't either in Neutral or Park. I don't think your truck will have the neutral safety connector though if you had a manual transmission. The purple wire that runs from your ignition switch to your starter motor is supposed to be routed through the neutral safety switch. It's not totally necessary, but is a good idea safety-wise.

Looks like you need to connect those green wires to the switch. The green wires need to connect to the two terminals that are not parallel and not really close to each other. If they are looped together, then I wonder if the previous owner installed a toggle switch on the dash or something for turning on the back up lights?

I bought a replacement Neutral Safety/back up light switch from Autozone about 6 months ago for $4.95.