Fred Redfast

I have a vacuum problem and it effects my braking. I have traced the problem to the vacuum pressure sensor on the left front fender well by the brake booster. When engine is running I only have 15 in vac and shut down it goes to 0. With the sensor disconnected and plugged I have 27+ in vac and at shutdown it hold 27 in vac.
my problem is I cannot seem to find this vacuum sensor, it is suppose to warn you when vac drops below 8 in vac by the brake light on the dash lights up.
is thisI a really necessary item of can I just plug it and do with out it??

thanks in advance.....Fred