How Do I Bench Test a Vacuum Relay? I bought a few vacuum relays new but want to test them. What Ive researched online, the instructions weren't clear, the videos dark and blurry or incomplete information. I have a MityVac hand pump thing. So how exactly do I do it? I dont trust alot of new products these days. Thx Steve

 

It looks like you are going in the right direction. What makes it tough is vacuum relays have 3 ports, one live vacuum port when engine is running, You can use the hand pump for that. Then you need another vacuum source to switch the vacuum relay (maybe your mouth with a hose attached or another vacuum source) that should activate (switch) the relay if it's working right. You might need a diagram for the vacuum port positions or look and see how the hoses were removed. So 1 is vacuum source, 2 is vacuum from switch, and 3 is going to the vacuum diaphram.