Need some help please. My girlfriend drives a 1993 Chevy 3500 diesel. Dually, 5-speed, dual batteries. The gauges keep acting up. It calls for a 20 amp fuse, which keeps blowing. I have gone as large as a 30 amp, but it also blows in a few seconds. How do I go about troubleshooting the gauge circuit? Recently, the battery was going dead. Alternator was putting out less then 12 volts( with a blown fuse) so I replaced the alternator. Getting 13.4 now. Thanks, Chief