Can anyone tell me what this part is for? It is connected to the body under the hood right below and behind the driver side hood hinge. It has a 3 prong electrical connector to it, and a small vacuum hose connected to it. It is a black disk looking part under a metal mounting bracket? I broke the hose barb off by mistake, and I don't even know what the part is for. Please help. Oh, it is on a '91.5 D250 intercooled. Thanks. -Jeff

 

I believe that is the low vacuum switch that turns on the brake light. I found one on ebay when I did the same thing...Mark

 

Vacuum sensor. Just plug the hose and unplug the electrical connector.

 

What am I turning off if I plug the hose and unplug the connector?

 

It won't turn on the brake light when you have low vacuum...Mark

 

Low vacuum switch.

Your first indication of a failed vacuum system will be durring a panic stop and you realize you are not slowing down, it will take both feet with all you have got to lock the brakes.
Been there done that and my light did work.

Jim