C2 - The "Tale of Two Alternators"

[Tom D.]

Partners:

Got a 63 250 HP running smoothly, but when I disconnect the battery ground cable it dies. I learned this test from the service manual. Testing voltage shows no change between battery voltage-not running and battery voltage-engine running. Measures usually 12.3 or so at all times.

This tells me the alternator is not putting out, right? I've taken two different 37 amp units to the local parts store (One was rebuilt fairly recently, and both test "good".) However, the test operator was young enough to be my grandchild.

Anyway, I've installed each in combination with the same new voltage regulator, same result.

Is poor grounding of the voltage regulator important enough to cause this? I added a second ground wire, but only tested that with the second alternator. I saw no change. I'm about ready to buy a remanufactured one, just to confirm the alternator is - or is not - the problem.

Tom Dingman
4889

[don 42616]

Re: C2 - The "Tale of Two Alternators"

Tom, at idle 12V+ is same at battery as engine off.

[Terry R.]

Re: C2 - The "Tale of Two Alternators"

If I remember right pulling the cable off trick only works with a generator.Good Luck Terry

[Tom D.]

The 63 manual says to pull ground off as test *NM*

[Jack H.]

Re: The 63 manual says to pull ground off as test

The manual is correct...car should continue to run with battery disconnected IF the alternator is charging. For grins, try one test...put a voltmeter across the battery, monitor voltage before you start the engine. Start the car, watch the voltmeter as you rev the engine to 2000 RPM. Does the voltmeter suddenly jump up? If not, the alternator is NOT charging the battery.

Now, why? The alternator is controlled (driven/paced) by the external electro-mechanical voltage regulator mounted on the LH inner fender. Early '63 cars used a Delco Remy '512 voltage regulator while later cars used a 'new improved' '515 voltage regulator. While not much is said about the change, I suspect there were performance/reliability problems with the original '512 design and that's why it was quickly superceeded/replaced with the '515. Original '512 regulators are HARD to find!

On the back or the alternator is a two conductor plug for the wiring harness to plug in. One of the two wires in this plug supplies the alternator's field winding power, it's labeled 'F' by an emboss on the case. That's the lead that powers up the alternator's field windings. If there's no current flowing through the field windings (bad contact/broken wire in the harness), the alternator can NOT produce electricity.

The other wire on this plug is the reference or 'sense' lead and the case of the alternator is embossed 'R' above the lead. It's how the alternator and voltage regulator monitor the current charge level of the battery. What the voltage regulator 'sees' on this lead is how decisions are made to turn the charging system ON/OFF.

By taking your alternator to a local shop for testing, you're leaving 2/3rds of the system behind! The voltage regulator has to be in good working condition too or the charging system isn't going to work. Also, the interconnect wiring has to be correct/intact too.

A full theory of operation + troubleshooting text for the Delcotron is given in Section 6Y of the 1963 Corvette Shop Manual. Any competent auto electric shop can attach their wheel-up diagnostic cart to the car and pinpoint the problem(s) in 15-minutes flat!

[Tom D.]

JH: Great Response - Thanks! *NM*

[Terry R.]

Re: C2 - The "Tale of Two Alternators"

I stand corrected.