2005 Cadillac CTS alternator testing

I have a 2005 Cadillac CTS with the north star engine. I need to find a wiring diagram for the charging system and the correct steps to diagnose it

Are you positive it's the Northstar engine? I can't see that the '05 CTS came with those, only the 2.8L and 3.6L Or, is this the CTS-V with the 5.7?

I took a guess and grabbed the 3.6L diagram:



Is there a specific symptom you're trying to diagnose? Trouble codes?

This system is fairly straightforward to diagnose for a no charging concern. The orange wire at the alternator is the L-Terminal, or the 'turn on' signal. This is usually a 12V signal from the PCM to the alternator to command charging. It's a steady signal with no pulse width control. As long as the alternator sees 12V on that wire (and the alternator is OK), it's charging. The grey wire at the alternator is the F-Terminal, a feedback signal from the alternator to the PCM on how hard the alternator is working. There are trouble codes associated with this circuit, but can't cause a no charging concern.

When the alternator suffers an internal failure, it grounds the L-Terminal, pulling the 12V down to near zero. When this happens, the PCM sets a trouble code and turns on the battery light. This makes diagnosis easy. With the engine running and no charging system voltage, backprobe the orange wire and check for voltage. If it's near zero, unplug the alternator connector and check again. If it's now near 12V, the alternator is toast. Voltage drop the power and ground connections, and make sure the belt isn't slipping before replacement.