Big_Ern

OK first off, Yes, 105 amps is overkill for our little cars, but these GM alternators are MUCH cheaper and easier to find than then 2nd gen ones that a lot of people seem to be swapping in.

I used a Delco CS130 out of a ’92 Buick LeSabre with the 3.8L engine. There are two alternators available for this car depending on whether it has the heated windshield option or not. The regular non heated windshield car comes with a 105amp alt, whereas the heated windshield has a 130 or 140 amp alt. Like I said before 105 amps is more than enough so I chose this one as it was cheaper.

I used a Bosch rebuilt alternator from the local parts store (Lordco). I don’t have the part # handy, but I could try to dig it up if anyone is interested. You could also pull one from a car in the junk yard, but I didn’t have the time to go looking for one when I did the swap.

You will also want to get the stock alternator plug with a few inches of wiring when you get your alt. This can be bought new, or again pulled from the junkyard (almost all 90+ GM & Chevies use the same plug so it’s easy to find).


First thing to do is remove your stock alternator.

Big_Ern

Next remove the serpentine pulley from the GM alt and replace it with the v-belt pulley from your stock alt. There is also a large spacer/washer in behind the pulley that you may need to swap as well. I swapped the fan as well, but I don’t think this step is necessary. The most important part here is that the pulley on the new alternator is exactly the same distance from the mounting ear as it was on your stock alternator or else you will wear out your belt prematurely. Double check this when you swap that pulley over as you may need to grind a little off the spacer, or add a small washer to make it thicker.

GM alt on the left, stock on the right.

Big_Ern

As you can see from the pics, the mounting ears are very similar. The main difference that you will notice is that the stock alt has 2 ears on the side that mount to the engine and 1 where it bolts to the adjuster. The GM alt has only one thick ear on the side that would usually mount to the engine, and a smaller one that bolts to the adjuster. However, to make this work we are going to bolt the one small ear to the engine and the large one to the adjuster.

Ignore the red wire for now; I’ll talk about that later…

Big_Ern

Test fit the alternator by bolting the small ear to the front of the engine mount much like the front ear on the stock alt would go. Take a straight edge (large ‘L’ ruler works great) and lay it across the center of the alt pulley and line it up with appropriate V in the crank pulley. You’ll notice that the ruler is not parallel and the other (large) mounting ear on the alt doesn’t line up quite right with the adjuster (Unfortunately I don’t have any pics of this stage, but let me know if you have any questions and I’ll try to draw something in paint).

To fix this you need to grind a small amount off of the back of the mounting ear as shown in pic 1. Depending on the size of the spacer you chose earlier you may have to grind of more or less than I did, so take of a small amount first and test fit again – you can always take more off, but it’s pretty damn hard to put it back on.

You may also need to grind a very small amount off of the front of the other (large) mounting ear (pic 2).

Big_Ern

Now for the fun part… Wiring!

The stock alt has only 2 wires, whereas the GM alt has 4. However, only 2 of them are necessary, so this part is fairly simple.

The stock alt has 2 terminals marked R and L (you can see the L terminal marked in pic 1). L is connected to the stock alternator warning lamp on the dash, and R is connected to a switched ignition source.

The GM wiring is as follows:
S – Sensor wire (connected to the battery or output terminal of the alternator)
F – not necessary
L – Same as our stock alt
P – not necessary


Run a wire from the S terminal on the new alternator to the output terminal of the battery as shown in pic 2. (note: I was not able to get a proper GM plug in time for my install so I used some female spade connectors instead. I do not recommend this and will be replacing it with the proper plug soon)

Finally cut off your old alt plug and solder the L wire to the new L wire on the GM alt.

Note: The GM harness is in the order mentioned above (S-F-L-P) starting from the red wire as shown in pic 2.

Big_Ern

Connect the v-belt back up and fire up the car and you’re done!

Big_Ern

Conclusion & Results:

My head lights are brighter (especially after the relay mod), my car starts better due to always having a fully charged battery, my heater blows harder, and my windows go up and down better. In short, every electrical device works better!

It probably sounds harder than it really is (I tend to complicate things when I do a write-up…). This mod only took me 1-2hrs from start to finish.


Modifications:

If you understand how an alternator works you will know that the S terminal is used by the alternator’s voltage regulator to sense what the current output is and regulate it accordingly. I wanted more power to the system so I tricked the alternator into thinking it was always getting a lower voltage by connecting the stock R terminal to it instead of from the battery. This works well in our older cars as the keyed ignition switch tends to be worn causing a voltage drop and thus puts out a slightly lower voltage than what the battery has. This causes the alternator to bump up the output voltage to make the new sensor wire have ~14V. You could even add a voltage divider circuit into the system to fake an even lower voltage at the alternator’s S terminal (which I did), but that is beyond the scope of this write-up and if you wish to know more you can search on Google or send me a PM.

Thanks:

Thanks to rotarydankus for the ideas in these threads:
https://www.rx7club.com/1st-generation-specific-1979-1985-18/alternater-upgrade-cheapy-253529/
https://www.rx7club.com/1st-generation-specific-1979-1985-18/electrical-issues-258903/


Questions:

If you have any questions or need a clarification, please post them here for the benefit of everyone else reading (I will subscribe to the thread so I don’t miss anything).

Kentetsu

Nice work Ern.. 1 vote for the Archive!

Re-Speed.com

iTrader: (3)

Great write up. I would also ad, you can go to any local alternator rebuild company a purchase a replacement regulator for the CS 130 that is self exciting. The new regulator would be inexpensive and eliminates wiring.

-billy

gsl-se addict

iTrader: (3)

Yes. Nice work. I would advise against connecting the R terminal to the S terminal on the alt, though. There have been many reported problems with battery discharge this way. The alt expects to see battery voltage at that terminal. When the car is off, the R terminal is at 0 v, but the output is still at battery voltage. The alt basically tries to charge with the car off. It is best to just run the S terminal to the output terminal or back to the battery + through a separate fused connection (this is what they did on the S5 cars). This info is based on what the S5/S6 alts do, but I am sure it is the same with the GM alt.

I agree having an upgraded alt is nice. I have an S5 in mine. Battery voltage is much more stable and everything electrical works better as you stated.

SCCAIT7

Do they make a one wire alternator for these cars? I am looking for one to use in a racing application....

OneRotor

iTrader: (3)

schweet. I've been looking for a cheaper alt. upgrade. Thanks for the writeup. adding this to the list of things to do this summer.

evil_motors

iTrader: (3)

sweeet.. can you get some pics of the actual wiring though please ? i am only slightly confused..

saltyslug

this is a good writeup. I am gonna have at least 10 55w lapms on my 12a baja, so this will come in handy. I might even step up to that 140.

Why are people not using the one wire gm alt? I have not seen one swapped.

If you have a big sound system this mod would be good and the 140 might be a good upgrade also. Start adding up what your accessories can suck and it adds up quick.

Re-Speed.com

iTrader: (3)

We used GM alternators in the one wire form for many years in rallying. Easy to install and just the one wire to the battery.

-billy

Big_Ern

apparently these newer CS style alternators are a bit more reliable than the older 1-wire. Plusd the wiring isn't that big of a deal. Connect the S terminal the the output and a wire running to an idiot light on the dash, or you could replace the idiot light with 1-3W resistor would work just the same, but it needs to see some sort of resistance to turn the alternator on.

Big_Ern

I have heard of this problem as well with the S5/6 alts, but I have not experienced this my my setup. I have an old weak battery and I often leave my car sit for 1-2 weeks with no problem starting it back up.

In my research on the swap I didn't run across this problem either. Maybe the GM alt are a little different? I could be wrong... so Disclaimer: do the S terminal mod at your own risk.

Another option would be to use a voltage divider circuit to artificially lower the voltage at the S terminal, but connect it to the battery rather than the old switched R terminal.

Big_Ern

If you did this 1-wire conversion the idiot light on your dash would stop working, and might possibly always be on due to it not being hooked up. Is it really worth it for 2 extra wires?

Big_Ern

I don't have any and frankly mine looks quite ugly right now because instead of using a proper plug, I just found a couple female spade conectors the proper size and jammed them in there so it wouldn't really show you much anyway.


Maybe these pics & simple directions will help.

- Find the wire going to the stock L terminal and connect this to the wire for the new L terminal.

- Cap off the wire for the old R terminal so it doesn't short out (this wire is not used).

- Connect the wire from the new S terminal to the output post on the new alternator.

- Cap off the remaining 2 wires (P & F) from the new alt as they are not used.

fishbulb95

Mmm 105 amps.... think of all the microwaves, and kitchen appliances i can power in my car!!!!!! Home away from home

Big_Ern

would have to be a fairly small microwave.

I think when the ar is running it probably uses 10-20 amps itself, so that leaves you with about 85 for acessories.

85Ax14V = 1190Watts

hmm I guess ~1200W would be enough for a decent sized microwave

fishbulb95

Sweet... well i'm not gonna be running the microwave while i'm runing the blender for mixing drinks....... wow i can see this going downhill very quickly.

evil_motors

iTrader: (3)

okay so to clear this up.. how many wires are plugged in? 1 or 2.. and the B+ terminal of the new alternator gets the old wire?

Big_Ern

2 wires as I mentioned in the post above, plus the main B+ wire, but I assumed that one was self explanatory

so 3 total

evil_motors

iTrader: (3)

okay cool i was just double checking.. thanks for this wright up..