1958 Buick Alternator Conversion
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I hate generators. They're bulky, don't put out any serious power at idle, and are a general pain-in-the-you-know-what on any regularly driven vehicle. They are even worse on an intermittently driven vehicle as the battery has a hard time staying charged because of the low power at idle problem of a generator.  Since I plan on driving my 1958 Buick Special a lot once it's completed, the decision to convert from a generator to an alternator was a complete no-brainer.

For the theory behind this, see my pages on alternator and generator theory, alternator conversions, and converting from a generator to an internally regulated alternator. For the "overview" wiring diagrams on this specific conversion, please see my page on maintaining the "push gas to start" with an alternator - that really helps explain the wiring for this.


Alternator Selection

For actual alternator selection, I chose a 63A internally regulated unit that was originally spec'ed for a 1973 Buick Electra. Why? Because I had some around to use as examples, they are readily available in parts stores (a remanufactured unit only set me back $35 + a $10 core), and because the 63A output is pretty close to the 50A max output of the factory generator system on the AC equipped cars. The last part is key - the factory ammeter and wiring is all the same for AC and non-AC cars, and I want to use the original ammeter - at least for now. This means I need to make sure it has some chance of not melting under the max possible output of the new alternator. The extra 13A is pushing it a bit on safety margins, though.


Alternator Mounting Bracket

For the lower alternator mounting bracket, I sourced one for a 1963/1964 401 cid Nailhead engine that did not have AC - it is the basis for this conversion. Unfortunately, the original 1958 "stud on bolt" arrangement does not work to mount the later bracket, so I needed to get the proper longer head bolts for the later bracket before I could mount the bracket. For the upper "arm" mounting bracket, I will be re-using the original generator piece if at all possible.

I did a basic sandblasting and "rattle can bomb" paint job on the bracket to get started. I think it looks pretty decent in black and will blend into the engine compartment nicely. I think it was the green engine color originally, but this isn't an original install.

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Here's the longer head bolts needed for the alternator bracket. Compare the later 4 3/4" long head bolts against the original 4 1/4" long "stud on bolt" arrangement for mounting the generator bracket and you can see the extra length, plus the longer "shoulder" at the bolt head. If you was to do this conversion but can't find the later model head bolts to use, you can use grade 8 7/16"-14 bolts of the proper length, but be sure you have enough threads on the bolts so they don't run out of threads when you tighten things down. I was lucky and found a pair of used head bolts from PAE Enterprises.

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Parts Removal and Original Wiring Harness

For actual work on the car, the very first thing I did was remove the generator, generator mounting bracket, regulator, and engine compartment wiring harness. Everything except for the harness will not be re-used, and the harness will be modified to work with the alternator. I do have a spare harness from a parts car, and I'm stashing that one away as the "pristine original" that will be safely tucked away in a box along with the generator, regulator, and mounting bracket in case I (or a later owner) even want to return the car to stock form. The harness is taped with vinyl harness tape, and I have the correct harness tape from other projects, so untaping it and retaping it with some changes should result in a reasonably factory-appearing harness.

As a side note, at roughly the same time as this work, I am also beginning a disc brake conversion on this car as well, and that will have some impact on the wiring - after the disc brake conversion I will not be using the master-cylinder-mounted pressure switch to activate the brake lights, and that means two fewer wires to come through the firewall. This bodes well for a later conversion of the instrument cluster to use modern electric gauges - I need some extra connections through the firewall for these. A possible later conversion to HEI would save one additional wire - the starter "R" terminal to ignition coil wiring goes inside the car and then back out again through another spot in the firewall to get to the ignition coil. The net effect of this is that the modified wiring will likely be significantly modified, so I might as well do it all at once.

The pictures below show the harness in roughly the layout it has on the car. In the first "overview" picture, the front of the car is to the left, the driver's side is to the bottom, the passenger's side is to the top, and the firewall is to the right. The other two pictures are details of the regulator and generator areas of the harness - these pictures are taken as if you were standing on the "side" of the car with the engine towards the top of the picture.

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The installation of the bracket and alternator proceeded reasonably easily. One small surprise was that I found out that the rearmost head bolt that goes through the alternator bracket is open to the water jacket on my engine. I know that because as soon as I removed the original head bolt in that position, I got a little fountain of green antifreeze out of the bolt hole. That's the cause of the wet area in the first photo below. The antifreeze fountain subsided quickly enough once I put the longer head bolt in and tightened things down, so no harm done other than needing to refill the radiator when I was done.

I also needed to get a slightly longer belt to use with the alternator - I found that a Gates 7545 works quite well for me. Due to the fact that the alternator is physically larger around and due to the way the bracket positions it, the center of the alternator ends up a tad further away from the engine than the generator was - thus the need for a longer belt. However, using the lower alternator bracket with the upper generator arm results in the alternator being positioned such that if you adjust the alternator very far "out" into the adjustment area, the belt hits the bolt head for the lower alternator mount. You can see how close it is in a couple of the pictures below. I sized the belt such that when the alternator was properly adjusted, it would be at the very start of the adjustment range. This means I had to completely remove the top adjuster bolt, get the belt onto the alternator, position a crowbar and hold the alternator in the "adjusted" position, and only then could I thread in the top bolt and tighten it down. I'm guess that using the upper adjustment arm from a later alternator equipped Nailhead - aka, an upper alternator mounting arm that matches the lower alternator mounting bracket - that the adjustment range is in closer to the engine and thus this does not occur. With the alternator adjusting arm instead of the generator one, maybe you could get by with the shorter belt. Basically, your mileage may vary, so pay attention and make sure everything works right.

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Modified Wiring Harness

The wiring harness needed some reworking to get the desired result. The regulator was completely gone, and now the starter relay wiring will need to run through the alternator, specifically using the field connection as a ground. To be sure this all worked right, I initially ran the wiring as individual wires and left them all long - this allowed me to verify everything was functioning plausibly correctly before I created a "final" wiring harness. If I needed to change anything, I could do so easily and without having to unwrap and re-do the whole wiring harness again. Once I get the final details sorted out and have the exact wiring I want, I can use that as a template create the final "nice neat and pretty" version of the modified wiring harness.

A related issue here is that the original large red wire in the harness (the main power feed to the car) is not going to work here - it's too short and has a terminal designed to hook up to the regulator. I needed it to be a bit longer and have a ring terminal suitable to hook up to the main battery junction post. The original wire also has an inline splice to feed power over to the horn relay connection, and I needed to replicate that. I opted to combine the remote voltage sensing wire and the horn relay power feed into one ring terminal to be connected to the main battery junction point. That puts a full set of 5 terminals there - battery, starter, alternator, power feed to the rest of the car, and remote voltage sensing wire + horn power feed - so it's getting a bit crowded compared to the original, but it should work out OK. If I could get one ring terminal to combine the 4 wires in the harness together (alternator, power feed to the rest of the car, remote voltage sensing wire, and horn power feed) then that would simplify things a bit, but I only have ring terminals suitable for 10 gauge wire, and evening combining the remote voltage sensing wire and horn power feed is a really tight fit into the terminal. You can see this in the first picture below - check out all of the red wires going to the same post as the large battery cable.

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One interesting/entertaining/"Doh!" note is that I had taken everything apart long before I put it back together, so figuring out the wiring again was a bit of a pain, especially the wires that go to the starter relay. One of them is completely new - instead of connecting to the "A" terminal on the regulator, it now connects to the field terminal on the alternator. Interestingly, this simple connection was enough to get the alternator charging in my initial testing, but I still have more testing to do and I need to run an alternator warning light inside the car and see if that changes things from my initial testing. Anyways, I took a couple photos of the wiring at the starter relay to remind me what goes where should I need to take this apart again. If you do this conversion, it's there for your reference as well.

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Also of interest is that I also opted to "remove" the ammeter from the main charging circuit. The main battery junction block now connects everything together (battery and alternator output) and power is fed into the firewall connector (and into the rest of the electrical system) via the position used for the original large "red" wire (on the driver's side of the firewall connector) - previously the generator output was all that flowed through the red wire. The large black wire is no longer used (in the middle position of the firewall connector) - previously the black wire connected the "battery" side of the ammeter to the main battery connection. Now everything is being fed in via the red wire and the ammeter is hooked up inside the car, but doing nothing. Simple and a bit crude, but effective for removing a high-risk item from the upgraded wiring without getting up under the dash and unhooking everything from the ammeter. I think this will be just fine because each of these two connectors is the same size and uses a 10 gauge wire which is plenty big for the loads applied to it. Also, I'm not increasing the load applied by the car's wiring. It was already running through one of those connectors (or both in some split percentage, depending on the actual load vs. the generator output at any given time), so I think this will be fine. In the photo below, you can clearly see the large red and pink wires, and that there is no black wire going to the middle position on the firewall connector.

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Here's a quick reminder of what wires are for what purpose on the small two-place connector that goes into a GM internally regulated alternator. The red wire (on the left) is for the remote voltage sensing feature. The white wire (on the right) is for the field connection. The plastic plus has a small "key" on one side to prevent it from being plugged in backwards, so it only fits one way. The terminals inside the connector are standard 1/4" Packard 56 style terminals and you can remove them and replace them with custom wiring very easily. See my Reusing Plastic Wiring Plugs page for more details.

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Page last updated 01/02/2009 01:51:39 PM