I have two ground wires from my engine block to the frame rail. One on each side. Then I have a 2ga. ground wire from the battery to the rear frame rail. If it isn't grounded well enough you will find out. Just try to start the car at night w/o any lights on. Any where you have a really close metal/metal point you could see sparks. Don't ask me how I know. My brother pointed this out to me one evening when he was visiting. I was getting an arc between my one header pipe and the inner fender. Not good. Put another heavier ground on the block and took care of that. Starter spins much faster now also.

Also go to NAPA and get a heavy duty fuse to put in your positive wire. I have a 300A fuse in mine. Yes it will still do some welding if the wire gets cut, but not as long as it would if it were not fused.