Several things could be contributing to the low output condition that you need to check, and correct that wonít cost much if anything.
1. Clean both battery terminals, and ground wire connection to block, clean ground strap connections between head & fire wall.
2. Grounding of all of the following devices needs to have zero voltage drop between battery negative terminal and each the deviceís outer cases; voltage regulator, alternator, and spark control box if you have electronic ignition. If you have voltage drop, it can be eliminated by connecting all the cases with a ground loop connecting one of the mounting screws at each device, so that one wire connects them all, and goes back to the battery negative terminal.
3. Clean the ground wire connection at each head lamp, parking lamp, and tail lights, and check for voltage drop from each of these ground points to the negative battery terminal.
4. Have battery load tested.
5. Is this a new, rebuilt, or junkyard alternator? Sometimes a diode or two will burn out (often right after someone pulls off one of the battery cables while the engine is running), which will reduce an alternatorís output. Have the alternator tested, and voltage regulator tested.
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC