Gremlin in wiring update

[Donald O.]

Hi all,

In my 67 convt L79, no a/c, no PW, with all the fuses in their circuits, I removed all three connections on the alternator and my ammeter read 0.00 amps. Reconnected the black ground lead and still no short. Reconected the plug-in connector (Dark Blue wire and White wires that go to the voltage regulator) and the short returned, 1.37 amps. Disconnected the connector again and the short went away. Reconnected the red lead (back to battery) and again no short.

How can I check the voltage regulator, it is an aftermarket solid state type.
Is the problem in the alternator itself and how do I check it? TIA

Don

[Jack H.]

Re: Gremlin in wiring update

What you see can/does happen IF one of the diodes in the 3-phase rectifying bridge inside the alternator has suffered junction puncture and has failed short circuit. There can also be 'insidious' cases where the fault is marginal and removing bias voltage allows the puncture to 'cure' until it again ruptures when passing/blocking current under voltage load.

I don't think I'd go further (pull the voltage regulator).... I'd simply pull the alternator, take it to a competent parts house with an alternator bench tester and have it run up. If one of the six diodes is 'toast', it won't achieve rated current output (it'll still put out but not at full rated current supply).

If I'm right, you have two alternatives at this point. Swap the alternator for an off-the-shelf rebuilt one (NOT a good idea if yours is original PN with matching date code), or rebuild the one you have. Diodes can be replaced individually.....

[Jack H.]

Re: Gremlin in wiring update

What you see can/does happen IF one of the diodes in the 3-phase rectifying bridge inside the alternator has suffered junction puncture and has failed short circuit. There can also be 'insidious' cases where the fault is marginal and removing bias voltage allows the puncture to 'cure' until it again ruptures when passing/blocking current under voltage load.

I don't think I'd go further (pull the voltage regulator).... I'd simply pull the alternator, take it to a competent parts house with an alternator bench tester and have it run up. If one of the six diodes is 'toast', it won't achieve rated current output (it'll still put out but not at full rated current supply).

If I'm right, you have two alternatives at this point. Swap the alternator for an off-the-shelf rebuilt one (NOT a good idea if yours is original PN with matching date code), or rebuild the one you have. Diodes can be replaced individually.....

[Donald O.]

Re: Gremlin in wiring update

Jack,
Thanks, I'll take this alternator to the local parts store and get it checked and if needed replaced. The original in a box in my garage.

Don

[Donald O.]

Re: Gremlin in wiring update

Jack,
Thanks, I'll take this alternator to the local parts store and get it checked and if needed replaced. The original in a box in my garage.

Don