OK, you should have a 2.4L not a 2.5L correct me if I'm wrong please (is not relevant all the cars use the same system). The voltage regulator is in fact inside the ECM (engine control module) they are very reliable so I would check wiring/plugs first, it sounds that when it is cold there is contact and when it heats up there isn't, if the light comes on in less than 5 seconds after starts the problem is there all the time, it takes few seconds for the computer to check all systems and take action or not if it takes more than that then check voltage at the battery as soon as the engine starts with the battery charged and before the indicator light goes on if possible, voltage should be between 13.8v and 14.4 or voltage climbing to this range at this time of the year and keep on watching to see if the voltage drops down as soon as the light goes on all this will tell you if it is the voltage control system (field) or if it is the ground/charging wire (high amps). I have in the past unplugged the computer and plugged it back and many gremlins have disappeared (poor contact). If after checking all wires and contacts the problem persists it should be the internal voltage regulator, me personally would connect an external regulator for any Mopar vehicle between 1968 and 1989 (non computer vehicle) but get a "heavy duty" regulator the normal duty will not be able to handle the field in the nippondenso alternator you have, you can even get an adjustable heavy duty regulator and set the voltage to your liking, also try to fit the regulator besides the battery or as close as you can, it has a temperature sensor inside to help with the proper charging of the battery so the closer the better, after that if the indicator light bothers you a resistor can be fitted to the original plug coming from the computer fooling it into believing that it is connected to the alternator it works 2 out of 3 times. Good luck and keep us posted