I researched a bunch on the GBCM on the 08/09 stuff. I have been trying to decide if I needed to keep this in the stock harness I am setting up for my Mustang swap. It looks like from what I've gathered there are a couple of options:
1. Leave it wired up as stock and it will vary output of the alt based on load sense. Anywhere from 11.0V-15.5V, controlled via the ECU.
2. Completely removing everything and leaving the alt unplugged will cause it to go to a fail-safe mode and charge at ~13.6-13.8. This may be enough for a setup but can be considered a little low depending on the demand of the system.
3. Purchase a device to command a specific PWM 5V output to a given charging output. I have noticed two options, one which is much cheaper than the other. A basic PWM adjustable module can be had on Amazon/Ebay for under $10. Set the frequency to 128hz and adjust the duty cycle per the below table for alternator output. Speed Max Innovation is the other option but at $140 it is much more expensive. It is a bit more discrete and you purchase it with a given constant duty cycle.
4. Change the internal regulator out for a 4-Pin AD244 style (requires internal modification). Doing so will require the standard 1 wire hookup usually seen on LS1 style alternators and output ~14.5V
The L pin is the command voltage pin. A 5V PWM signal is sent from the ECM/BCM at a frequency of 128hz. If the duty cycle is less than 10% or more than 90% or just plain not connected, the alternator will go into default mode and put out about 13.7 volts. Enough to keep your car running, but not enough to charge the battery well. Here are the voltages and duty cycles:
10% = 11.0 V
20% = 11.56 V
30% = 12.12 V
40% = 12.68 V
50% = 13.25 V
60% = 13.81 V
70% = 14.37 V
80% = 14.94 V
90% = 15.5 V
Maybe this will help a few folks out. With all of that said I'm still not certain which direction I am going to go here
example below is of an early vs late:
- early vs late alternator.jpg (30.97 KiB) Viewed 109 times