55.2-59 Battery draining

[mr48chev]

Originally Posted by Phungki

So I was able to get back out there tonight. I have a -13.08 parasitic draw.
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The diode is a one way check valve for electricity that lets power go though that diode in the exciter wire to the alternator to tell it to charge but blocks electricity from feeding back from the alternator to the ignition. This is to prevent the feedback from keeping power to the ignition when you turn the key off.

Normally people either use the idiot light for the alternator or that diode to prevent the feedback. That is the fix for "I just put and alternator on my truck and drove it and it charged great but now the engine won't shut off when I turn the key off.

There should be no power though that wire with the key off. None=0

There should be no power at the pin for the exciter wire on the alternator with the key off.

This is how many of us who aren't putting in a complete wiring kit install an internal regulator Delco alternator


The white band on the diode shows which way the power flow goes.

There are two sets of diodes inside the alternator. The diode trio and the diode bridge. One or the other of those is what usually goes bad. They can be tested by taking the alternator apart but most parts houses don't keep them in stock. 25 years ago I was told by the counterman in a NAPA store that I was the only person in the area still rebuilding his own alternators. It isn't that common for an individual to do that anymore even though for someone with training and experience the degree of difficulty isn't that hard.

These diodes are again one way check valves for electricity

The tri diode


And or the diode bridge or Rectifier.


Those two from Summit cost almost as much as a lifetime guareentee alternator from O'Reilly's" That is why folks normally don't rebuild an alternator at home unless it is an "original" to the car or truck unit with the correct numbers that it left the factory and you are doing a 100 point restoration. Or you are cheap like me and hunt down the discount price parts and rebuild your own.

I really don't want you to take it apart because then I will have to write out a lengthy set of instructions and have to go take one apart to add photos to those instructions. I can do it and may do it as a separate tech thread some day.