What kind of car and have you done anything to the wiring like upgrades?

The factory old mopar wiring had a wire running from the battery, through a fusible link, through the bulkhead, through the ammeter, (branching off under the dash for other power also like the Ignition switch, headlights, etc.), back through the bulkhead and to the alternator.

A common short is the ammeter. If the car is running it can burn from the fusible link to the alternator. Also check the alternator and for a dead short in the ignition switch.

While hunting shorts it's a good idea to use a circuit breaker in place of the fusible link to save yourself money and trouble. After it's all good you can go back to a fusible link.