The "Play 2 Credits" button is the same as a "Max Bet" button for your game.
When lit up, depressing that button SHOULD turn the lamp off & play a spin.
That lamp will remain OFF until the game is finished (win or lose) , then the lamp will come back on....unless you hit a jackpot win over the max amount the machine is set/allowed to payout....in that case, you'll have to turn the jackpot reset key to clear the win.
If it doesn't light up after a normal spin/game, then I would check the wiring underneath the button deck to see if the switch wire fell off.
The two wires on the side of the switch run up to the lamp.
Yours however, IS lighting up sooooo....>>>
It's the other two wires that you need hooked up correctly to the switch.
Those two wires should be hooked up the same as the "Spin" button switch nearby.