Upgrading your alternator from externally to internally regulated

As part of the wiring upgrades on my car, I'm switching from the old 63amp, externally regulated, alternator to a newer style 100amp, internally regulated alternator hooked up using the 3-wire setup.

If you want to run the new alternator as a 1-wire alternator, which most people really don't think is a good idea on a street car, then the install is easy. The only problem you may see is that you need to rev the engine higher in order to get the alternator to kick into charging mode. Many companies, such as Chevy2Only or Mad Electrical, offer an adapter you can plug into your unmodified voltage regulator harness that jumpers the wires on the 4-wire regulator plug to allow the car to run properly without the voltage regulator hooked up. Once this adapter is installed all that's left for you to do is mount the alternator on the motor and run the charging cable from the alternator to your battery.

The old 2-wire connector on your old alternator will no longer be necessary and the plug on the back of the newer style alternators is different anyway, so you can't plug it in without modifying it first. I'm not going to attempt explaining this, first because the 1-wire setup isn't street friendly, and second because I didn't do it this way on my car, so my advice would ring hollow in my own ears. It's up to you to figure out what to do with the unneeded and dangling alternator pigtail.

One nice thing about the alternators advertised as 1-wire alternators is that most of them appear to be capable of being wired up as 1-wire AND 3-wire. It's up to you which installation you want to pursue.

Since I'm doing the 3-wire, internally regulated alterator conversion, I think I can offer more detailed advice on doing this properly. This will be the second time I've attempted this. My first attempt was on a friends 67 Chevy II that hasn't melted down yet and continues to charge the battery properly more than a year later. <grin>

This conversion really isn't that difficult. It does require a little bit of knowledge about the wiring harness in your car and some wire splicing skills. Neither of these are difficult to pick up. I would recommend a GOOD wiring diagram for your car. Most assembly manuals have correct wiring harness diagrams for your car in them that are very detailed and just about guaranteed to be accurate. Another source is aftermarket wiring diagrams. I found one on Ebay that was in color, which has helped greatly and it's a bit easier to read than the B&W one in the assembly manual. One other tip I'll offer is to invest in a soldering iron and some good wire connectors. While the crimp on connectors are serviceable, you'll get more stable performance and a longer life out of connectors soldered onto the wires you modify as part of this conversion. I just pull the plastic insulators off of the crimp on connectors, then crimp and solder them onto my connections. Yes, it takes longer, but it looks better and won't leave you stranded somewhere. Shrink tubing is your friend, I heartily recommend using it also.

Ok enough rambling, I'll get to the point on this conversion.

Let's start by showing off the new alternator. This will help give you a frame of reference for the modifications.

What we're seeing here is a 1-wire/3-wire alternator that can be wired either way. I've got the alternator pigtail already installed as well as a ground cable (8gauge braided wire at the top of the photo) and the charging cable (4 gauge braided cable on the bottom left).

What you'll most likely see when you pull one of these out of the box is no wires attached to it and a small black plug where the white and red wires are exiting on this one. The alternator pigtail is available at most auto parts stores, either in the Help! section or behind the counter. It's a very common part, is easily found, and is cheap.

If you're wiring the alternator as a 1-wire alternator, you will be leaving that little black plug in place to protect the inside of the alternator from contaminants. If you're wiring it as a 3-wire alternator, which I assume you are if you're still reading this, then you'll need to remove the plug and plug in your brand new 2-wire alternator pigtail.

The pigtail should have two wires, one slightly larger than the other. The smaller of the two wires runs to the idiot light in your dash that warns you when the alternator isn't charging properly. The other wire is used for voltage sensing and is typically connected to a power distribution point somewhere in your engine compartment that is fairly far away from the alternator. By running the voltage sensing wire to a distribution point away from the alternator and battery, you're taking advantage of a phenomenon referred to as voltage drop. Because wire isn't infinitely conductive, part of the voltage running through it is lost to resistance in the wire which leads to a voltage lower at the end of the wire than it started out with at the beginning. By sensing the voltage at the end of another long circuit (like the horn relay), we can force the alternator to produce enough voltage to compensate for the drop and provide the voltage we really want. If we sensed it at the beginning of such a circuit (like right at the alternator charge post), then we're making the alternator think it's doing enough work, but the effective voltage at the end of the wire is lowered by resistance and isn't as high as it should be. The moral of the story here is make sure you hook up your voltage sensing wire to the place in the system where you think you might see the lowest voltage. This will force the alternator to put out enough juice to provide adequate power at that point.

This picture might explain it a bit better, I hope.

More to come, this document is still under construction....