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 This 65 Chevys...  This 65 Chevys stock wiring routes the alternators output through the horn relay (arrow). From there, a charge wire runs along the core support to the battery, and main power to the dash harness branches off that. Additional leads from the alternator tell the external regulator when the battery needs charging and how much juice to supply. |
 We connected a new 8-gauge...  We connected a new 8-gauge charge wire directly from the output post on the back of the alternator to the batterys positive post using a pigtailed battery cable (A). Another pigtail (B) runs from the post to the stock power-distribution post (C) on the firewall to provide power to the rest of the cars wiring through the old charge wire. |
 The Powermaster alternator...  The Powermaster alternator can be wired either as a one-wire unit or a multi-wire unit depending on your needs. We chose the multi-wire configuration so as to maintain the factory idiot light and automatic charging functions (see One Wire or More? sidebar). In this configuration, the white wire hooks directly to the wire running from the dash-mounted warning bulb. The other pin on the regulator is a dummy, so the red wire can either be removed from the connector plug or looped onto the output post. |
 With the new wiring in place,...  With the new wiring in place, we removed the external regulator and its related wiring from the firewall. We left the original charge wire in place (A), which now serves only to route power from the power-distribution post on the firewall to the horn relay and the rest of the dash wiring, so it carries a much lower load. The other post on the horn relay bus bar (B) can be used as an auxiliary power source, such as for the headlight relays shown here. |
This is not an article about installing an alternator. Read a Chiltons manual if you need instructions. Its also not an article about how to rewire an alternator. Ask for a wiring diagram when you order the alternator if you need that. This is an article about how to tell if theres something wrong with the alternator you already have in your car and what to do about it if there is.
Recently we installed a fuel-injected GM Performance Parts Ramjet crate engine in our 65 Chevy Biscayne. In doing so, we added an electric fuel pump and a computerized ignition control, both of which require a reliable source of electric power to operate properly. So what did we do? We put the original externally regulated 37-amp alternator back on ita unit thats lucky to put out half the amps at idle that the fuel pump alone demands. That doesnt leave too much extra juice for the radio, headlights, or that engine-controlling computer. OK, we knew that was stupid, so before we took the car on its maiden voyage, we chucked that stuff and spent 40 bucks for a new 61-amp alternator and a new voltage regulator. But even that high-amp unit has it limitations. Its 61 amps only come at peak demand when the battery is almost fully drained.
And it puts out far less at idle than a decent modern alternator. Frankly, as the testing outlined in this article shows, we might have been able to get away with that setup as long as everything stayed in good working order and we didnt run the car too often with the high beams, radio, and wipers on at idle. But if we ever wanted to add an electric fan, air conditioning, or any other electrically operated accessories, it would be a different story. At a minimum we wanted to convert the antiquated wiring and external regulator to a newer-tech GM SI-series internal unit, and while we were at it we might as well step up to a high-quality aftermarket alternator rather than rely on the rather hit-and-miss quality and reliability of a parts-store rebuild. We called Powermaster and learned that theres a lot more to building a reliable charging system than just buying an alternator.
So, no matter what brand of car you own, if you want to learn about one-wire alternators, voltage drop, charge wires, amp draw, circuit testing, and pulley ratios, read the rest of this article.