Flickering head lights, what am I missing

Simulated interrupting the relay ground, the 86 terminal.
I disconnected the relay ground from the existing ground terminal then added in a alligator clip jumper to re make the connection.
Started the motor and moved the rear bumper mounted battery disconnect to Off, the engine continued to run, I then removed one end of the temporary alligator clip jumper and the motor immediately died.
So that will work,
Thanks
I will run the alternator field relay ground wire to one small terminal on the disconnect and connect the second small terminal to a good ground.
Question ?
Should I have a fuse on the ground wire? Either on the long run from the under hood relay to the rear bumper disconnect or on the shorter run of the disconnect to the ground?