Re: Delco Alternator Wiring - Reversed Terminals

Posted by Bob on December 30, 2004 at 16:27:34 from (66.163.134.177):

In Reply to: Delco Alternator Wiring - Reversed Terminals posted by Jim Bloss on December 30, 2004 at 15:17:20:

The reason it didn't shut off was that a "idiot lite" or diode is needed in the wire from the ignition switch to the "1" terminal of the alternator to eliminate alternator charge current backfeeding to the ignition system when the key is switched "OFF".

Also, charging current was PROBABLY flowing the same way, and bypassing the ammeter, and that was why you were not getting a "charge" reading.

I you leave it as you have it, it will almost certainly discharge the battery while shut down overnight, or over a day or two.

The #1 terminal is correctly called the "excite" terminal, NOT the "field" terminal.

During the transition from the old externally-regulated alternators to the internally regulated alternators, a number were built with a "dummy" voltage regulator installed that brought the "R" and "F" connections out through a plug which connected them to an external regulator in the same manner as the older series of alternators.

Newer-style alternators so-equipped have the 2 termianls side by side [II], unlike the internally-regulated versions that have the terminals edge-to-edge [--].

The 10SI or 12SI alternators have dual labeling on the terminals (F1 R2), but the "R" an "F" markings are a carryover from those transitional alternators and do not apply to the internally regulated units.

If you want to know what your alternator is REALLY doing, use a QUALITY digital voltmeter or a good analog voltmeter, and check the voltage at the battery. (Some lesser-quality digital meters cannot cope with the electrical noise generated by the ignition and charging systems, and will give "wild" readings, if they work at all.)

After sitting without charging for a while, the battery voltage will read about 12.5 Volts.

After starting, if the alternator is working, the voltage will come up to between 14 and 14.75 Volts, and the regulator will control it there.

Here's a link to a site with GOOD Delco alternator info:

• MAD electrical

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