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Alternator Conversion

I wanted to upgrade the electrical system by adding a high amp alternator and eliminate the voltage regulator... but I didn't want to just do the typical GM 10si or 12si conversion. That style of alternator just looks so "out of place" in a car like this. So I searched around quite a bit until I discovered Denso and Nippon-Denso alternators. These alternators are used on many cars - Denso on Chrysler and others, Nippon-Denso on many Japanese cars. They have a cool look, in my opinion, that sort of looks "old fashioned", and looks quite appropriate under the bonnet of a Healey.

The particular alternator I got was actually an aftermarket model I found. It has 10si guts inside it - Proform Part No. 66438. I used this one because 1) I could get a real good look at it before buying it, so I could tell the mounting points looked good, and 2) figuring it would just use standard 10si wiring, I'd be a bit more familiar with it when rewiring everything (I've messed with lots of GM cars in the past).

The picture above shows what my conversion ended up looking like (you can click on the picture for a larger version).

To the left of the v-belt: These are the brackets and spacers I made. Creating them was sort of "fit on the fly" - holding the alternator where I wanted it, taking measurements, and adding a piece at a time until it all fit right. The longer bracket with the long slot in it - this is the original lower Healey bracket, which I just lengthened the slot on slightly. If anyone wants to try doing things this way, I'm including PDFs of the crude CAD drawings I made for the brackets... but keep in mind that I did have to tweak some of the thicknesses and lengths a bit upon final fit... so your mileage may vary. Here they are...
1. <bracket and short spacer> 2. <long spacer>

The belt was just "measure and fit" once I got everything in position. I had an old really long v-belt laying around from some other car, so I started cutting it up, trimming to length and wrapping it around the pulleys until I got it where it seemed right. Then I simply measured and found the closest belt at the parts store.

Upper right in the picture of course is the Proform Part No. 66438 alternator.

Lower right in the picture - that's the original coil bracket, with one of the "legs" cut off. I did this so I could reposition the coil behind the alternator.

Below are some pictures of what the installation ended up looking like...

I did away with the external voltage regulator, but left it in place as a connection block. I gutted it, and then soldered a connection between the two terminal connection sections so that the whole thing was positive.  For wiring...


  1. I capped off the BLACK ground wire that formerly went to the "E" terminal on the regulator.  The regulator box doesn't need grounded anymore, but I wanted to keep the wire in the same approximate position for appearance.

  2. I joined the field wire and generator light wire together.  This is the small YELLOW/BROWN wire and the small GREEN/BROWN wire that were formerly connected to "WL" and "F" on the regulator.   I joined them at the voltage regulator, but not connected to the regulator... just kind of tucked up behind it, again to retain appearances.

  3. I gutted the box and added a "bridge" inside that joined both sections of terminals.  This makes the whole box positive.

  4. The giant YELLOW/BROWN wire that went to the generator now connects to the BAT. terminal on the alternator, still coming off its original "D" terminal on the voltage regulator... this thanks to adding that bridge inside and making the whole box positive.

Check out this photo for details...


The alternator has 3 connections - two come out of the plug in the back, and then the 3rd one is the big terminal that attaches via a nut to the side.  On this particular alternator, the two coming out of the back where RED on the "IG" terminal and WHITE on the "L" terminal.  Here's how I wired things:

  • RED "IG" - Connected this via a short length of wire to the (+) side of the coil.

  • WHITE "L" - Connected this to the original GREEN/BROWN wire.

  • BAT. TERM. - Connected this to the existing fat YELLOW/BROWN wire (goes to "D" on the voltage regulator).

Doing all this gets the battery charging properly, and keeps the generator light working properly. Here's a photo that sort of shows what the wiring ended up looking like...

FYI, those two wires coming out of the alternator - they're coming from the "IG" (ignition) terminal for the red one, and the "L" (lamp) terminal for the other, but those labels aren't actually on the alternator anywhere. You'll notice, if you get an alternator like this, that there are actually two more terminals coming out of it that aren't being used on the green adaptor plug. They are for computer/monitor stuff, not used in an old Healey application.

If anyone has any questions about any of this, send me an email!


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