I have a 1982 Ford F250 2wheel drive with carbureted 302. There is a cable that runs from the relay to the wheel well were it is held in place by a metal clamp and the cable sleeve was cut away and touching this metal clamp then continues onto the the engine. Is this necessary to to this? would it be good enough to ground to the engine. I only have one battery while looking up cables at local parts store web sites they mention 2 battery system cable set up that requires theuse of 2 different size wires needed. What is the 2 battery set up? Were my wires rigged to replicate this system even through I see no reason for them to.

 

That is the frame ground before going on to the engine block.
It is used for the trailer ground for its breaks and lights.
Also if you do not have a rear bumper it grounds the rear plate lamp.
It may also ground the tank selector solenoid on the frame.

If you have one fuel tank, a back bumper and do not pull a trailer then no you do not need it.

But do not forget that you do need a good 10 GA body ground from the neg post to sheet metal of the body.

 

You can't have too many grounds. If you want to get a new ground cable that does not have that feature, I would run a 10 gauge wire from the frame to the engine block or from the frame to the battery neg terminal.