[kipps]

The gen 4 engines use a three wire "battery current sensor". This functions as an ammeter, and is clipped on the negative(sometimes the positive) battery cable. All three wires from this sensor go directly to the BCM. The BCM talks with the ECM through the GMLAN data lines, and tells the ECM how to adjust the alternator output.

You have several options. Listed below from best to worst.

1. Use the gen 4 alternator with the BCM and current sensor.

2. Swap the gen 4 alternator for a gen 3 alternator. This allows it to internally regulate the voltage.

3. Swap the voltage regulator within the alternator for the gen 3 version. This effectively converts your gen 4 alternator to a gen 3 style. However now, you no longer have an off-the-shelf alternator for easy replacement.

4. Use your gen 4 alternator with no BCM or current sensor attached. Leave it wired to the ECM as stock. It will enter a "fail-safe" mode, and will continuously charge at 13.8 volts. Many folks do this out of simplicity. This will theoretically compromise battery life, charging capacity, and fuel economy.