I just bought a 1986 F150 300 inline 6 and noticed a black box with a big white switch that moves left/right it has a metal tube that comes out the back of it and goes into the engine compartment but isn't hooked up to anything, anyone know what this is?

 

It's a DUI breathalyzer.

 

It could be a old timey trailer brake controller. The old ones actually hooked into the brake line at the master cylinder. The lever is a manual control where you can reach down and manually apply the trailer brakes only.

 

it was a brake controller, I found the manufacturer on the box which was the only marking on it and found out what it was that way! thank you guys