Installing an Amps gauge?

I would like to install an amps gauge in my car, but I don't know where you hook it up. The gauge has the letters by three connections S, G and I on the back. Could someone help me?

The Amp gauge must be installed between the “HOT” post of the starter solenoid and the “BAT” terminal of the key switch (on the tilt-column of a in-dash key-switch - whichever is applicable.

STEP 1: Connect a 10-AWG (minimum) Red wire from the 12-volt terminal post of the starter solenoid to the “I” post on the back of the gauge.

STEP 2: Connect another 10-AWG (minimum) Red wire from the “S” post of the AMP gauge to the “BAT” of the key switch (on either a tilt-column or an indash key switch).

STEP 3: Connect a 16-AWG or 18-AWG Black wire from the “G” post on the back of the Amp gauge to a ground connection behind the dash.

STEP 4: If the pointer Amp gauge reads “backwards” (indicating “discharge”) when
you know the alternator is “charging” simply reverse the two wires connected to the “I” and “S” posts on the back of the gauge in STEP 1 and 2 above.

IMPORTANT: DO NOT allow any “ground” wire or other “ground” to contact either the “I” or “S” terminal of Amp gauge at any time! A ground contact to either terminal could result in major electrical damage or fire to your wiring harness, other electrical components or to your vehicle.