I would read this mad article
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
and seriously consider doing away with the ammeter
There's a very good thread here on how to modify your cluster for a voltmeter
http://www.forabodiesonly.com/mopar/showthread.php?t=119480
Read the entire thread, as it covers different style clusters
This might be a good time to consider relays. I used a box out of a Voyager which gave me relays for ignition / injection, charging system, lights, and left over for security system
I believe you'll have to string a separate wire to wire up the original "IGN2" circuit, that is the coil bypass. Even if you don't use a ballast resistor, you'll need that as "IGN1" goes dead during "crank."
Other little tidbits might be.............Might be a great time to consider (depending on your ignition system) hiding a kill switch so the car cannot be easily hotwired. If you use an electric fuel pump / relay, you can use a switch in the relay circuit, and most thieves would never figure it out "in time."
You can easily make the car impossible to drive off, but if they show up with a roll back or wrecker..............