All GM alternators since the CS130 was deployed for use in 1986 to whenever the 2 pin garbage of the 2000s started have a Terminal,
P, which can be used to get a tach signal. There are situations where there are things mounted externally on an alt and read a wheel, but Idk about gm on that one.
Not all GM alternators that are CS130 however internally hooked up the P terminal, thus you couldnt use them for the alt but there was another pn alt with a different plug(the smaller side so not the large end which is a sense, but the small one which is P for phase now had a wire). It's possible the phase terminal "P" is not connected internally.
Get a DMM, set it to measure AC voltage with at least a 30V range, and measure between the P terminal and ground with the engine running. This will tell you if the P is internally connected to one of the stator leads.
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S is the big side, sense, it may or may not be used from factory on your truck, L is probably not, but it depends on if your ECM has any monitoring/say over your charging system, I/F depends on the same thing. if its I not F, a charge light or a resistor provides the excite signal, if its F the PCM would provide the resisted ignition. P is your tachometer wire which you need to see if yours is wired to do so if you are unsure
It could probably be modified by you easily since relatively simple.
But. A CS130D or an AD230 is probably(dont know for sure) wired internally already and they have better reliability, lifespan than the CS130 and they use internal fans (safety for your hand while playing with your truck) they also have better outputs. Cheap too
they also are wired the same way you just need a new pigtail or a conversion pigtail to wire them
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The engine RPMs and the alternator RPMs are proportional and change based on the amount of throttle you provide, which varies from idle to WOT. Meaning you dont have to worry about pulley sizes changing it. but you want to make sure all grounds and your sense wire are used and good. Just so the internal math doesnt have to account for swings from poor hygeine
TO MY understanding, the tach you have now is driven by AC voltage. If so, that is how your tach can be driven with the alt. If its not driven by AC, you will need a tachometer which you can buy a one that sits on your column usually
