Take a DMM (Digital Multi-Meter)or a Digital Voltmeter and try this.

Test Conditions: Engine Running (head lights, blower, hazards ON)

Checking Ground circuit integrity
Connect the meters POS lead to battery NEG post, connect the meters NEG lead to the Alternator bracket. Set meter to DC Volts, >.500mV you have ground circuit issue somewhere.

Checking Positive circuit integrity
Connect the meters POS lead to battery POS post, connect the meters NEG lead to the POS lead at the terminal block located at/near the Auxiliary water pump. I believe your alternator harness should make a connection at this terminal block. Set meter to DC Volts, >.500mV you have a positive circuit issue somewhere.

The results of these tests should give us a better idea of how we can help pin point the cause.