First off make sure you use a constant duty solenoid. A regular ford solenoid wont work it gets hot and quits. Don't ask me how I know. On the solenoid the one small terminal goes to the switched side of the cut off switch and the other if it has two and it's not case grounded goes to ground.

I have a pic of how I did mine but can't get to it right now.

Here I found one.