Of course I can only speculate but it sounds like power is not getting through the bulkhead to the interior.
All power is routed via the heavy RED wire cavity #16 labeled Battery in the diagram below..
After passing through the bulkhead connections power then goes to the ammeter, another weak point.
I'd test for power at the fuse block on the terminal labeled BATT (lower left), if not getting power there you can be sure there's a bad connection, probably burnt or corroded at the bulkhead.
If that's the problem the best solution is to bypass the bulkhead & ammeter, instructions found here
http://www.madelectrical.com/electricaltech/amp-gauges2.shtmlNot sure what you mean by ignition relay but if your referring to the starter relay on the fender by the battery I'd suspect either a starter that's drawing to many amps, should be 180-200amps, or a bad cable running from the relay to the starter... had many Mopars & not a single starter relay failure or starter for that matter...