I just got in from driving an 85 f250 6.9 home after buying it. I have no idea what this thing is and didn't really think to ask about it when I was looking it over... I was more concerned with underside and engine...

so here is a pic. imgur: the simple image sharer

it mounted under the dash on the drivers side.

 

That's an electric brake controller for trailer brakes. Good to have when towing a heavy trailer.

Congrats on the purchase! How's she run & drive? Any more pics of the truck?

 

she runs great! the guy I bought it from said the glow plugs need replaced and that only one or two work so I probably wont be able to start it when its cold. so I'll get to them after the vac pump. but I'm super excited to finally have a truck now!

more pics later. I'm going to go clean it here in a few. There was a literal rats nest in the glove box...

thanks for the advice earlier