The version you're describing, which has a wire from the S post of the alternator to the S terminal of the regulator, is for an ALT light setup. These are wired differently. In this setup, the keyed power source goes to the I terminal. The S terminal acts as a "ready" signal from the alternator to shut the ALT light off once the alternator starts to charge.

If you have an ammeter, there is no connectivity between the alternator and the S terminal of the regulator. The S terminal of the regulator simply gets a keyed power source. Nothing goes to the I terminal.