Under dash short

Tonight we were cruising down the highway at 60 MPH in our 71 Dart, engine shut down and before I could coast to a stop we had smoke coming from under dash. Got hauled home and discovered main power wire from starter relay to ammeter connection fried at fire wall. Ran wire through bulkhead connectors to replace burnt terminals and thought I had problem solved, no such luck. Still have dead short some where that caused bulkhead terminals to melt. Can ammeter cause this? Wiring diagram indicates power goes to fuse panel, horn relay, headlight switch and ignition switch connector after ammeter. Any idea what could have shorted out going down the road?