OK - you want a step by step procedure?
1 disconnect the battery ground.
2 connect 2 shielded jumper wires to the Battery meter terminals, one to each terminal - and let the ends hang to the floor of the car.
3 reconnect the battery ground.
4 connect a ($4 at Harbor Freight) multimeter in 0-20volt mode to one jumper wire end and the other to ground (e.g. the instrument cluster) to get a reading of about 12volts.
5 disconnect the multimeter from that jumper lead and connect the other jumper to get a 12volt reading there too.
6 If you do not get a reading of approximately 12volts from either jumper, the wire that doesn't have 12volts is not connected to the horn relay or the starter solenoid. Find the break in the connection to the Battery meter.
7 if both sides have a reading of about 12volts, start the car and check the readings at both jumpers again (steps 4 and 5). One of the jumpers (the one connected to the wire from the horn relay) should read higher than the other. If it does, and the meter does not move, replace or repair the meter.
8 Post here again to tell us the results.
PS: if the meter is damaged, and you are installing the repaired/replacement, you may want to install a 1 or 2 amp inline fuse on one of the terminals as noted in the help area near the bottom of this web page: http://www.corvetteforum.net/classics/magicmachine