If an alternator has bad diodes, would it show as a parasitic draw when tested with amp meter?

Question

1987 Toyota Pickup. We Charge the battery up overnight and put an amp meter between the negative pole on the battery and the negative cable. It shows no draw untill we open the door or something. If the alternator was causing the problem wouldn't it show up as a parasitic draw when we test it in the above fashion?

Answer 1

Yes. Actually, any draw from any other source should also show up using the method that you describe.

The fact that an alternator doesn't show a draw from the battery is not an indication that the alternator is operating correctly and charging the battery properly. Put a simple volt meter across your battery and start the engine - you should read 13.8-14.2 volts at approximately 1500 rpms.

Answer 2

This could also happen at altitudes above 5000 feet and South of I-80 if both of these are true you will need to move to avoid getting parasites in your battery.

Answer 3

it should not show a draw until something comes on like the dome light.

a parasitic drain could show up this way if it was substantial enough.