This article is from the Chrysler-Plymouth-Dodge FAQ, by Dr. David Zatz with numerous contributions by others.
Check the battery cables, then check the alternator with a test light
and/or a voltmeter or an alternator/charging system analyzer. There are
usually four connections on a Chrysler alternator, one large terminal
(power out), one ground, and two field control wires. To check the field
control wires, test both for voltage with the engine running. One should
show battery voltage, the other a reduced voltage. If both show battery
voltage, the problem could be in the computer (not providing a ground for
the second field circuit). If one has battery voltage and the other shows
a much reduced voltage, the computer probably is trying to "full field" the
alternator and therefore the alternator is probably the problem. Check
output voltage. If output voltage is extremely high (20 volts or more)
check the circuit from the output terminal to the battery for an open. If
the voltage is battery volts but not a charging voltage and the fields seem
correct, suspect the alternator.