inertia switch button question....

[MercRS]

My 86 McLaren the pump quit yesterday didn't know about the inertia switch
somebody told me about it he reached in there hit it and it was fine.Today
I was doing the rear brakes and the same thing happened.I went to hit the button but nothing happens,does the white button snap down? and I know my
batt is weak but the button you just push down right?

Thanks