Give us a little more information. Are you saying that the ammeter shorted out internally or that there is a short somewhere in the electrical system that you need to find?
What did your ammeter do that makes you think it is shorted? If an ammeter shorts internally between the terminals it usually just stops working but everything else will work, unless it shorted to the case. If it failed open, then everything except the starter will be dead. You can usually bypass the ammeter. What lead to this? It is possible you may have more problems than the ammeter.
Check with Greg Long about where to find a replacement.