GREAT NEWS....and bad news...

If you don't have one you need to get a multimeter before you try starting the car again and really burn something up. A digital multimeter sufficient to trouble shoot car electrical systems can be purchased for less than $20. The multimeter will have DC voltage settings for measuring the elctrical system and resistance settings to check for continuity and look for shorts.

Since you have the engine running I would guess you have the MSD box hooked up correctly but to check; The purple and green wires hook up to the two pick up wires from the distributor. The small black (-) and orange (+) wires attach to the coil - and +. The large black wire needs to connect to a soild ground, I attached mine to the block near where the MSD box is mounted. The LArge red needs to attach to a constant 12 v battery source. I hooked mine to the same terminal on the starter relay as the 10 gauge wire from the (+) side of the battery. The small red wire needs to be connected to swiotched 12 volts. Now that is easier said than done on old mopars. Everything that is switched on with the key in the run position is off in the start (engine cranking) position except for the ignition and that position bypasses the ballast resistor. The best way to hook up the small red MSD wire is to hook it to the blue wire that would normally be connected to the (+) side of the coil. You don't need to bypass the ballast resistor but bypassing it elminates something that can fail. On my car I just took a piece of 18 gauge wire and put male spade connectors on the ends. Just plug it into the two connectors that would normally plug on to the ballast.

A quick word about grounds. If you have bad grounds all kinds of gremlins will rear their ugly heads. You should have a solid 8 gauge or larger ground wire from the engine block to the firewall. I also have another ground wire from the (-) of the battery to the radiator core support. I also use toothed lock washers under the fasteners that attach the grounds to ensure I have bite into the base metal.

I am assuming the alternator you had rebuilt was a pre 70 style alternator and you still have the pre 70 style voltage regulator. The regulator needs a good ground (remove the paint where the regulator contacts the car and use toothed lock washers. This style of system works by switching voltage to the field windings of the alternator. The newer style has two field connections with one being switched 12 volts and the regulator controls the path to ground.

You trouble shoot the charging system with your multi meter on a DC voltage setting that will read to 20-30 volts. With the engine running and the volt meter across the battery terminals you should read 13.8-14.1 volts. Reving the engine to greater than 2000 rpm may make a momentary increase in voltage but it should come right back to the voltage at idle. And, turning on all your lights, wipers, heater blower, radio, etc can make a dip in the voltage but it should come back to the 13.8 to 14.1 volts by reving the engine to 2000. If it perfroms this way and you still have the fuse blowing issue after a few minutes then there is a short occuring some where. Real close examination of the wiring and using the multimeter on a resistance setting looking for a short will be required. If you haven't trouble shot short issues before you should enlist someone with some experience to help.

If you get a high reading (15 +) when measuring the the voltage across the battery but it otherwise it acts as described above you have a bad connection somewhere that is casuing a voltage drop. Measure the voltage at the power terminal of the regulator is shouldn't be any more than 1/2 a voltage lower than the voltage across the battery, same with the voltage at the output terminal on the regulator. If it is larger than 1/2 volt then you have some bad connections. The output of the alternator goes through the bulked connector to the amp meter and from the amp meter back through the bulked connector to the starter relay to the battery. Makes sure all those connections are clean and tight. The regulator gets its power through the ignition switch, fuse panel and bulked connector any one of these connections can cause enough voltage drop to cause the regulator to over charge.

If when measuring the voltage across the battery it varies directly with rpm and continues to rise with rpm then the regulator is not working. Check the regulator ground. Also, the regulators are cheap enough (around $10) at the local parts store its not much point messing with them.

If you disconnect the the regulator from the alternator and it still outputs voltage (more than 12.8) then the alternator internally has an issue.

NOTE: if the alternator is not a stock mopar type alternator then some of these instruction don't apply and I would need to know what it is to help.