gauges going crazy when starting the car

they settle down to normal operation...or continue to go berserk....have a mechanic wirebrush the main 1/0 battery connection...I suspect that the ground to the chassis is "iffy" and the gauge panel cannot tolerate varying voltages from below 12.5 volts goin' up and down in a random fashion because there is limited potential electrically...bad ground....clean the ground...get a NEW battery if older than five...will screw up the alternator charging a battery that won't take a charge~

OK as soon as it quits raining like monsoon style I will give it a shot. Thanks