To be sure the "electrical is not causing" the rough idle, simple yank one field wire off in order to disable the charging system, and if necessary, charge the battery
Then run a clip lead from the starter relay stud or other battery source directly to your ignition system. On an points or ECU system, this is the "key side" of the ballast, IE opposite side from the coil
IF the problem goes away, the charging system OR WIRING has something to do with the rough idle. No1 suspect is the BULKEAD CONNECTOR
Please read this article by MAD electrical:
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
It shows, whether you perform the modification or not, the pitfalls of Mopar wiring
This problem could be SEVERAL things
Bad bulkhead connector terminals.
break somewhere in the alternator charging wire and connections, including the BULKHEAD and the AMMETER, as well as the "IN HARNESS SPLICE"
Bad alternator, either worn or stuck/ damaged brushes, or other internal problems
Bad connections in the "igntion run" circuit, which ALSO supplies the regulator and field circuits
Bulkhead connector, ammeter circuit, igntion switch and its connections.
Some tests
Run a temporary wire either no10 OR LARGER, or maybe three or 4 no 14's in parallel directly from your alternator stud to the big stud on the start relay
The ammeter will NOT work, but measure with a voltmeter, observer your idle, and action of lights, heater, and see if this improved problem.
Hook a temporary wire no14 or so directly from starter relay stud to ignition system/ regulator and see if this makes a difference.
WIth key in "run", engine OFF, measure the voltage drop in the ignition suppy harness
To do this, hook one meter probe on the battery positive post, the other lead where your "dark blue" "ignition run" supply hooks, you can access this at the regulator "I" (ign) terminal or the "key side" of the ballast
What you are hoping for is a VERY low reading. Anything over .3V (3 TENTHS of a volt) means you have a poor connection in the igniton feed
The circuit path is battery -- fuse link -- bulkhead connector -- ammeter circuit -- ignition switch connector -- through the switch -- back out the switch connector -- back out the bulkhead (dark blue "run") to the regulator, the ign. system, and on 70/ later cars, the alternator field.