I am planning to do a new wire harness installation on my 1977 F150 and have started to create a wiring diagram for what is in place today. I am not sure what the function though is of this ball shaped object in my engine compartment. I had thought it was initially the horn but I do not see any electrical wires running to it. I appreciate any feedback.

 

Looks like a vacuum diaphragm.. the other ends goes too ? Brake booster ?

 

Vacuum canister. Used on most cars to keep climate control operating properly on acceleration. No vacuum equals default to defrost.

 

It runs through the firewall behind the brake booster. I have not yet pulled the dash apart enough to trace where it is connected.

 

Tyoder is probably correct if it runs through the fire wall.

 

Thanks guys! I appreciate it.

 

You bet. That engine bay looks really clean for a 77

 

Thanks, someone before me did an ok job of cleaning and painting it. I just bought it a couple months ago. They likely painted the engine bay the same time they painted the body green. From what I can tell from inside the door panels and dash the truck was originally red.

 

Had one on my 78 Ranchero that looked like a tin can painted black. It too had a single vacuum line going to it.