I have a 99 dodge 3500 diesel and last week the ignition switch went bad so I replaced it and now it starts just fine but volt gauge won't go past 10. Used multimeter on wire in back of alt and it reads 12, also the heater blower stopped working and it lacks power I'm at a loss here pls help....

 

Have the alternator tested to make sure its pumping out at least 14 volts. If not, there's the problem. But if the alternator is fine then understand that the alternator does NOT regulate voltage, the PCM does. So if the alternator is charging correctly then look at the PCM.