How difficult will it be to locate a bad ground on a 1999 442 baja with triple engines? besides batteries constantly running down, the only aspect that did not work correctly was the fuel gauge, when running a wire to the neg on one of the batteries it fixed the Gauge?? no manual or anything to go by how much trouble am i in?? Are there any more manuals out there that can help me?

I have not seen any manual out there. Sounds like you have some wire tracing, multimeter and standing on your head time coming to you.

For the running down batteries, I would start by disconnecting some accessories: bilge pump(s) (they might be stuck on), lights, radio, power points, ignition, Switches, gauges, main battery switch, ect. Wile unhooking each item, use your multimeter on DC amps and see if the draw drops or not. When it drops you have found the problem, and you can work on replacing/why from there.