Most common problem is a broken wire in the shift lever. The switch easily pops out of the lever handle. Take it out, and put an ohm meter across it and push the button to see if it makes contact. If not, replace the switch. If it does, put a jumper wire across the contacts in the shift lever to see if that makes it "activate". That would rule out bad contact in the socket. I don't have the schematic in front of me, so I don't know if it goes to a fuse, or directly to the control module. If there is a fuse, then check it. Last resort would be to jumper the input at the control module. If this activates the light, then you know the switch actuation is not making contact from the lever through the wire to the module.
