[Whaler]

Skip the gauge for now..use a multimeter on the battery itelf.
The charging circuit can be checked by measuring the voltage across the battery while the engine is running at about 2000RPM. The voltage should be about 13.5 Volts and should alter only a little when you put all the lights on.
Make sure you do have a line connected between that new alternator and the positive side of the solenoid/battery...You may not be getting the alt output to the battery.

Do this first then we go from there. It seems you have replaced most of the charging cct by now

Tim