Greetings. I have a 1967 Olds Delta 88 with the 425 engine. I want to replace my current alternator, which has an exterior voltage regulator, with one with internal reg. Does anyone know which gm alt.I need and will fit? Thanks.

 

Any 12SI Delco alternator bolts in. Easiest thing to do is buy the 95 amp version used on the 1986-88 Olds Custom Cruiser with 307. Obviously you need to change the wiring.

 

The upgrade you’re thinking of is a great fix. I’ve done 2 ‘66 big cars this way and never regretted it. Follow the design posted here. In my order of preference, front disk brake upgrade is just ahead, HEI is just behind.

GM decided in the mid 70’s that internally regulated was the way to go. After a few decades evolving from generators & external voltage regulators to the 10SI and 12SI designs. For mid-60’s big Olds cars, 1975 technology is the sweet spot for compatibility with the 1960s, but the advances that were better. An internally regulated alternator is one of those advances.

Physical compatibilty
The 10SI will fit better physically than the 12SI. You’ll have fewer alignment & modifications to make. The 12SI can be made to work but you’ll burn time figuring out how to notch mounting brackets and making the belt align. I suggest you buy a new alternator with the same or very similar (not more than 90° off) clock position. On the other hand, you’ll be modifying the wiring anyway, so decide on your preferences for safety & replacement convenience.

Upgrade the wiring
Factory systems of the mid-60’s max’ed out at about 65 amps. These days, some of us add electric radiator fans & stereos which draw more amps. So you might need an alternator with a higher output to avoid drawing down the battery in a rainstorm, with the radio on, in traffic. If you go with higher amperage output, consider using a thicker wire - 12, 10, or even 8 gauge for an output wire. Run that fat cable to the junction block with full confidence that the thicker wire will have less tendency to heat up under load and melt over a hotel intake manifold causing a short.

The 10SI & 12SI have a field and “sense” wire in addition to the output cable. As I recall, the best location for the “sense” wire was to run it to the junction block too. The “sense” wire tells the alternator what the voltage is across the entire car. Hooking it to the junction block gives a good average voltage value to the alternator to tell it to charge the system or not.

The “1 wire” replacements basically trick the internally regulated alternators into believing that the output from the alternator _is_ the system voltage. That’s wrong, because, uh, wires have resistance. More or less this overstates the voltage level across the car. It’s probably not fatal, but why not do it right? I recommend avoiding the 1 wire alternators for a car you want to keep.

When you get into the wiring, use the same colors the factory did to the best of your ability. You’ll be happy a red or purple wire runs where the diagram says 5 years later when you have forgotten this upgrade. If you can, use the same color shrink wrap as the wire. If you can’t color match the wrap to the wire, use clear shrink wrap.

Formal soldered & shrink wrapped connections
Considering that the alternator & battery are critical systems, I’d avoid the “crimp it & it’s done” approach. I recommend factory-correct “Packard 56” male & female metal spade connectors and the correct plastic shells for reliability. Just like GM did. Slip the color-correct (or clear) shrink wrap up the wires before you solder your terminals. Then solder. Yes it’s time-consuming. But the payoff is years of reliability. I have no problem with generic spade connectors color coded by size, but the for something as important as an alternator, why not spend 20% more time to get it really right?

Take your time
The older I get, the more I realize I rushed too many of these projects when I was younger and needed the car back on the road.

If you can, take your time to do it right. As in, imagine your the wiring harness engineer in 1964, designing cars for 1967. What would you do to make these cars be reliable, simple, simple to repair and robust? At least for me, that’s a fun challenge.

Let us know how we can help from here. Hope this helps.

Chris

 

Third motion on using the SI type alternators and snagging a 95A late 80s 12SI version and calling it a day. It was very early on after finishing the Cutlass production of 1988 that they started using 95A 12SI for everything. In fact, that immediately became the "replacement" for the OEM 78A version in the GMSPO system. The internal regulator alternators actually first appeared in limited applications in 1969 as a 10SI used in various amp ratings, and notably in the 69 442. These early "open-faced" alternators are highly sought after and usually EXPENSIVE if you find one, but not as simple and reliable as the later models. There are reports of very late '68 applications, but that might be a factor of someone reading a date code of 1968 and not realizing the 69 model year started in late '68 and with parts manufacturing lead times...anyway, I've never seen an original '68 GM car with an internal regulator.

12SI is easier to find and a heckuva lot better than the 10SI version. It's built with higher amp ratings in mind and better cooling pathways and fan. Easy to spot with a large round air exit fan on the front.

You will need to change the pigtail on the alternator end of the sensing wires attaching to the internal regulator obviously, but that's easy-peasy. But as mentioned, solder the connections for maximum efficiency/life.

Here's a good read on the 10SI and 12SI alternators and their differences.

Catalog

The main thing is to make sure you have the right clock position for the regulator plug. If you know how to work on alternators, then get whatever because they're easy to "re-clock" as you need. Just need the socket for the 4 case bolts and a toothpick in case you pull the back half too far off and the brushes pop out. I think on your car, your pivot bolt is at the bottom and the belt adjusting bolt is on top, so if you get a 3:00 position, your regulator plug would be on the inside closer to the engine. If you want easy access to it as it would be exposed, you get one at 9:00 position. Your choice.

EDIT: Reverse those plug clock positions if you don't have A/C. I assumed you had A/C.

 

Thanks so much for the great info. I am amazed not only by the incredible knowledge that you all have, but also your willingness to share it. I know it takes time to compose your thoughts and to send it, so again, thanks. I will go with a 12si, 95 amp, as it sounds like a better version of the 10si. I was thinking about a one wire, but it sounds like I should go with the three wire. I'll let know how it works out.