You didn't answer --- you have a shop manual? wiring diagram? test lamp? meter?
Usable diagrams from "MyMopar:"
(These diagrams are not always complete or correct, but usually better than nothin)
http://www.mymopar.com/downloads/1971/71DartA.JPG
http://www.mymopar.com/downloads/1971/71DartB.JPG
which came from here:
http://www.mymopar.com/index.php?pid=31
You can download a 72 shop manual here for free:
(Look through the thread, there's a 71 wiring diagram there)
http://www.forabodiesonly.com/mopar/showthread.php?t=132309&highlight=manual,+download
Read this article, mostly for the simplified diagram:
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
posted below:
As others posted, follow the diagram. The battery junctions at the "big stud" on the starter relay. From there a fuseable link takes off and feeds power INTO the interior of the car, represented by the red wire in the diagram. It then goes to the ammeter, through the ammeter, back OUT the bulkhead connector on the black charging wire, to the ammeter
Check with your light/ meter. IF you have power at the start relay "big stud" and NOT at the alternator output stud, the problem is between those two
Your top suspects are:
bad fuse link
bad connections in the bulkhead connector
bad/ loose connections at the ammeter, or something wrong with the ammter
(The ammeter MUST be hooked up or the wires hooked together to get power in the car)
might be a damaged "in harness" "welded splice" In the simplified diagram, that splice is taped up in the under --dash harness, to find it, untape the harness following the black ammeter wire (the only large black wire with a ring terminal)