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Delco (GM) Alternators for XJ-S

Delco (GM) Alternators for XJ-S


The other night, I had an interesting drive home in the Jag after dark. As you know if you've been keeping track, I have a Mercedes electric fan and a GM electric fan, both connected (for the time being) to the same circuit so they both come on with the A/C compressor, and I also have four 100W headlights -- all of which adds up to a considerably higher current draw than the car was originally designed for. It was relatively cool out, so the A/C compressor was cycling in and out. Each time it would cycle on and bring on the electric fans, the headlights would dim, the blower fans would slow audibly, and the voltmeter would drop about 1/8". Clearly, the Lucas alternator isn't keeping up with the load. Time to retrofit a GM alternator with higher current capacity!

Shopped around today, and am herein documenting some of the things I learned for possible addition to the book. Posting to the list as well, both for the benefit of anyone who may wish to do a similar retrofit and in hopes of garnering input from anyone who may have corrections or editorials to add. Anyone who doesn't care about GM alternators should hit "Delete" now, if you haven't already.

There are lots of variations of GM alternators, but for our purposes there are five basic "types" that we might consider for the XJ-S: The SI-10, the SI-12, the SI-15, the SI-17, and the CS130. All five mount in the same basic way, which is NOT the same way the Lucas alternator mounts. This is why such a retrofit either requires the John's Cars alternator mount or yanking the air pump and mounting the alternator where the pump was, as per Napoli's instructions in my book.

When talking about GM alternators, positions of the adjustment lug and the regulator terminals are defined as follows: look at the rear of the alternator with the pivot lug pointing downward (6 o'clock). The vast majority of GM alternators have the tensioner lug at 12 o'clock, but they can also be had at 2 o'clock or 10 o'clock. The regulator terminals can be any which-a-way, but why anyone would care I dunno. Also note that the pivot lug itself can vary somewhat, with some models having a "long" lug. For XJ-S applications, I think any pivot lug configuration will work, and the 12 o'clock tensioner lug should work as well as any.

The SI-10 comes in amperages up to about 70, and can be rebuilt to put out over 100 -- but the shops I talked to don't recommend this, and generally refuse to do it. Apparently when this alternator is set up for high current, it won't charge worth a rip at idle, and they get nothing but complaints from customers that try it.

The SI-12 looks to the untrained eye to be the same thing as the SI- 10 -- in fact, many of the parts are interchangeable, and one shop told me that they occasionally get rebuilds in that have SI-10 and SI- 12 parts mixed up in the same alternator. One visible difference is that the SI-10 has a metal fan blade while the SI-12 has a plastic impeller that looks like a solid disk with openings around the edge. The core parts of the SI-12 are much better than the SI-10, though; this alternator comes standard up to about 108 amps, and can be rebuilt to put out 140 amps -- a very common rebuild for folks that have high-power sound systems in their cars. It reportedly charges just fine at idle.

The SI-15 is physically quite a bit larger than the SI-10 or SI-12, and the SI-17 is difficult to tell from the SI-15. These typically can be had up to about 108 amps as well. Didn't get a lot of info on these, but a suitable unit can be purchased by going into a Discount Auto Parts or Pep Boys and asking for an alternator number 70897. It's cheaper at DAP but the core charge is higher, so if you'll be writing off the core charge (I'll be damned if I'll give them a working Lucas for less than $40) the way to go is to go into Pep Boys, tell them what DAP wants for the 70897, and get them to match the price and charge you their core charge. You'll end up spending around $100.

When fitted with an internal regulator (the only configuration that should be considered for the XJ-S, since the Lucas is also an internal regulator type), all four of the alternator types above will come with three terminals. One big one is the obvious main power connection that goes directly to the battery. The other two are numbered 1 and 2 and connect to a standardized plug. Terminal 1 connects to the battery, which means it is a simple matter to connect it to the big terminal -- I couldn't get a straight answer why this connection wasn't made inside the alternator, but perhaps it has something to do with fault diagnosis. Terminal 2 connects EITHER to the idiot light on the dash OR to a switched ignition power supply, depending on the alternator and the car, but apparently any and all of them will work connected to an idiot light. Also of note: one shop showed me an alternator with a blank-off cover over the terminals 1 and 2, claiming you don't really need to connect anything to EITHER of them, but if you want to you can just remove the cover. There are also a few alternators that come with one extra terminal for connection to a tachometer.

The CS130 is the newer GM design, used on 90's cars; there is also a CS121, but it's hard to tell the difference, and apparently cars with fried CS121's are advised to replace them with a CS130. It is smaller than ANY of the alternators above. It has TWO cooling fans -- one metal fan on the front, and another fan inside the housing at the rear. In stock form, they generally put out 105 amps, can be rebuilt to put out 140 amps, and reportedly charge like a sumbitch at idle. They are ALL internal regulator type, which you'll need to know -- apparently they assume you know that, because none of the books or catalogs tell you.

A suitable 105-amp CS130 can be had by asking for an alternator number 1352-1-11. The numbering scheme includes info: the -1 means a 1-groove pulley, and the -11 means the regulator connector is at the 11 o'clock position. You'll end up spending about $100 again. In fact, one shop told me that their pricing scheme is simple: $1/amp.

The CS130 alternators come with some interesting variations in main power connections. There are some that are rectangular. Whatever, it shouldn't be difficult to finagle a connection to the battery in the XJ-S.

The CS130 comes with a new kind of regulator connector: a rectangular block with four terminals in it -- one large one and three smaller ones. The big one goes to the battery again. Apparently, the small one right next to the big one goes to the ignition switch on cars without an idiot light. The middle small one goes to an idiot light on cars so equipped. I dunno what the farthest small connector goes to, but it might be a tach connector. In any case, in the XJ-S you only need to connect the big one to battery and the middle small one to the light to get the alternator to work in the XJ-S.

Auto parts shops sell a variety of connectors to fit the CS130 regulator connection. There are plugs with all four wires. There are plugs with only three wires. There are plugs that adapt to the 2- wire connectors for retrofitting the CS130 into cars that came with the earlier alternators WITHOUT idiot lights, and plugs that adapt to the 2-wire connector for retrofitting the CS130 into cars WITH idiot lights. Your choice, about $5; three out of these four will work on the XJ-S.

I had ONE place tell me that the CS130 is not as reliable as the earlier models, but it wasn't a source I'd put a lot of stock in; I'd be interested in feedback from the list on that issue. As it is, if I don't get input that changes my mind, I'll probably go with a 105- amp CS130, since a shop I *was* impressed with assured me it was the best way to go.

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