Trying to resolve some high idle issues and such what kind of wire should I use as an additional ground as has been suggested in various posts
You can buy a ground strap at most auto parts stores, available in various lengths. It needs to be attached to the engine and the other end to the chassis. On the V12 XJ-S, one good place to put a ground strap is between a bolt holding the power steering pump to the engine and a bolt holding the front anti-sway bar inner bushing to the chassis. Others choose to attach the ground strap right up on top of the engine somewhere so they can easily see that it’s still in place and doing its job.