still could be the alty (if a rebuilt and not totally new). You'll need a meter to run the tests but if the battery's current draw is high enough, might be able do it with a small low wattage (12v) incandescent test lamp instead?
Battery's negative terminal is disconnected and test lamp (or meter) is placed between clamp and battery terminal. If lamp is glowing - it means a high current flow. Pull fusible links until lamp goes out and report back on which link did the trick.
