Curious about two things. My truck does not have charging issues or anything like that, but going down the rabbit hole on alternator-driven tachs is making me as this question-

Section 1 - S terminals:
On most wiring diagrams for a 2g alternator, I see the S wire from the voltage regulator being connected to the S terminal on the connection of doom/B+ output plug. My truck has no provision for an s-wire on the fire plug, and has/had only wires going to the A and I terminals on the voltage regulator. I've never had a problem with charging, although running voltage is lower than I would expect at ~13.x volts. I replaced the ASI plug a few years ago, and just kind of have the S wire dangling/capped.

The questions I would have here is: Why does the S terminal jumper not matter on this truck? Or does it and someone in this truck's life didn't care?

Section 2 - Stator output:
Does the S terminal on the voltage regulator send or receive signal from the stator? I am curious if this would suffice to send signal to a tachometer?

 

To answer my own question: On a diesel engine, the S terminals are not required. The S-terminal output on the alternator was used to power the electric choke on gasoline engines.

 

But you forgot to indicate the solution to the tachometer feed. My tack has been dead for several years after performing the tach mod which didn't last.

 

Ah, yes. The Stator output will provide a signal that can be used for a tachhometer. The s terminal on the regulator is not an output.