Open the hood--all the way up (i.e. vertical). Look on the top of the engine on the passenger's side and way back by the firewall.
You'll find small black box on the end of a wire. (It may have fallen down in; you may have to search around).
The black box has clips on two sides and a hinge on the third side. Unfasten the clips and lift the hinged cover--and there be the pushbutton and the LED.