Preparing to re-wire my 55.2 gmc 100 with a 350. Pulled this thing out of the dash, it was to the left of the steering wheel. Nothing was attached to it behind the dash. The button does press in. Appears to be some sort of vacuum device?

https://flic.kr/p/rDSk5L

https://flic.kr/p/sjiyvG


1955 GMC 100 Series 2