to test a fuel gauge you need a potentiometer. the gauge works off of resistance. from 30 ohms to 240 ohms in most cases. radio shark or frys will have one and you just hook it up to the sender wire and ground. turn the dial back and forth and the gauge should move. if the senders are bad, they're like $30 for new ones and they just drop right in. you might have to pull the tank out a bit to get enough room.
that being said, make sure your tanks are grounded. both for the gauge reading AND for safety. especially your fuel fills. there should be a small ground from the battery/motor to the tanks sender (you can attach it to the screws that hold the sender in, and then from the sender to the fuel fill. reason being if its not grounded when you go to fill up the tank it touches the fuel nozzle it could spark and that would be bad. especially if your tanks are touching carpet. all that foot rubbing creates tons of static electricity.
as far as the tach with points? ditch that crap and slap a HEI in it. u can get a "billet" hei distributor for like $40 with coil and it'll work all day long. hook your tach sender wire and an ignition 12v and bam, done deal go boating!
