Battery not charging - tell me what I'm missing

[RichardJ]

Vettevet has the fuses circled in this thread. http://67-72chevytrucks.com/vboard/s...se#post6219269

Alternator voltage is dependent on several things. Battery state of charge, temperature, and engine rpm effect charge voltage. The small 37 Amp, EX reg Alternator can put out about 20 Amps at idle rpm. The SI alternators can only put out a maximum of 25 Amps at idle and again, that is only if the battery needs it.

Full fielding an alternator is a viable test. It should only be done for a second. The voltage will shoot up to 16-18 volts and the load will drag the engine rpm down. That's all you need to know.
You should use 12 volts from the battery or from Regulator terminal #3. The idea is to eliminate any possible problem from the Regulator and terminal #4 does not do that.

The externally regulated alternator has one side of the field always grounded. The regulator controls the voltage on the other side of the field winding.

The SI alternator has one side of the field winding always connected to 12 Volts. The regulator controls the ground side of the winding. Grounding that side, bypasses the regulator to test the Alt only.