Holy freekin wiring diagram, Batman
First, go download this shop manual which AbodyJoe posted
[ame="http://www.abodyjoe.com/pictures/Misc.%20car%20info/70%20Dart%20Challenger%20Serv%20Man1.pdf"]http://www.abodyjoe.com/pictures/Misc.%20car%20info/70%20Dart%20Challenger%20Serv%20Man1.pdf[/ame]
Sometimes these diagrams from MyMopar are incorrect and incomplete, but they are also sometimes easier to follow. "An alternative."
http://www.mymopar.com/index.php?pid=31
Two diagrams:
http://www.mymopar.com/downloads/1971/71DartA.JPG
http://www.mymopar.com/downloads/1971/71DartB.JPG
Now, it's possible that your problem(s) may be a couple or three different ones, or related and caused by the same bad connection, etc.
Let's take stuff one at a time.
In the manual AbodyJoe posted, get into the wiring section, page 8-1 and onward, and look up the bulkhead connector layout. This will tell you "which wires are what."
You want to identify
1--The igntion "run" wire, IE what is powered with ignition switch "on." This comes out of the bulkhead connector, and feeds several components under the hood, the alternator blue field wire, the regulator "I" terminal, and the "ignition switch end" of the ignition ballast resistor. If you have a FOUR PIN ballast, that wire feeds the end of the ballast that is jumpered together
2--The coil bypass, which is usually brown. This comes from the switch, through the bulkhead, and to the coil + end of the ballast resistor. It is HOT in "start" and is the only source of ignition voltage in start
3--The "start" wire, which comes from the switch, through the bulkhead, and to one of the "push on" connectors on the start relay. This is hot only in start and is what activates the relay for start
4--The second "push on" relay connector goes down the firewall and to the neutral safety switch on the trans. It is very possible the shifter is not going far enough into park, but you can temporarily wiggle the shifter around NEUTRAL to get around this problem
A---So take your test light and probe the starter relay yellow/ yellow tracer, twist the key to "start" and see if you have power. If you do, remove the one going down to the trans, and ground that terminal with a clip lead. The engine should now crank, but be CAREFUL as it will crank "in any gear."
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Four vs five pin boxes:
The five pin boxes are OLDER, and unlikely you'll find a new on to buy.
The older 5 pin box MUST have a 4 pin resistor
The newer 4 pin box CAN use EITHER a 2 or 4 terminal resistor, it's simply that the "other half" of the resistor doesn't do anything, is not connected
You cannot tell a 4 pin box from a 5 by looking, always, because some brands of boxes STILL HAVE 5 pins, it's simply that the 5th pin is not hooked up. An ohmeter is needed if you need to know.
The resistor has a "U" shaped cutout on one end. It is important to get it installed correctly, as (actually 2 resistors in one enclosure) are different values. The "U" is a "key"
It is VERY important that the ECU and regulator be properly grounded. Make sure there's a good ground jumper from the battery to the body, and that the regulator and ECU mounts are scraped clean, and tight bolts, USE star lock washers.
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Examine the bulkhead connector for corrosion, looseness, and heat damage. Unplug the connectors, inspect them, and "work" them in/ out several times to scrub the terminals
Do the same with the ignition terminals. Pull the distributor connector, the ECU, and the regulator connector, and the ballast connectors. Inspect them, and work them in/ out to scrub them and to "feel" for tightness.
