I fired up my 56 BelAir restomod for the first time Saturday, and the alternator was putting out 17 volts. Pulled the connector from the alternator and it is putting out 13 and change, just like it should. What purpose does that orange wire going to that connector serve? It clearly is not necessary to excite the alternator, as it charges fine with it disconnected. Before I just clip and cap that wire, I just wanted to understand the purpose of that wire. I am using a gen 5 corvette accessory drive. Thanks in advance.


Regards, John McGraw

 

If I’m not terribly mistaken, that’s a PWM signal to regulate output voltage. The alternator will put out a higher voltage if the ECM sees that the battery needs help, or if your running a lot of electronics in the vehicle at one time. On the other hand, you’ll see the gauge drop way down when cruising and the ECM senses that battery is good and needs no help…also less work needed by alternator will help fuel mileage, which is GM’s goal here. My Silverado does this.
This is the complete connect and cruise setup, with ECM, correct?

 

I knew the late model vehicles used the PWM. but I thought that they were limited to cars that monitored the current draw on the system. Clearly, the connect and cruise setup is not that sophisticated. When I look at the PWM duty cycle table, it tops out at 15 volts while my alternator goes to 17 volts and sets the MIL for voltage too high. I have checked the voltage on the wire when key is turned on, and it only goes up to less than a volt and drops to 0 volts when key is off. I am going to guess that this would indicate a problem with the alternator and not the harness or ECM. Since the alternator goes to the default output with the wire disconnected (13.5), it looks like the alternator only goes high when turned to the "on" setting. If anyone has any more info on the connect and cruise setup. I would appreciate the insight before I go out and purchase another alternator. I could just leave the wire off the alternator, but I would rather have the alternator charge at a full 14.5 than the default 13.5 setting.


Regards, John McGraw

 

As I suspected, the regulator was the problem. Popped a new regulator in it and it is charging right at 14.25 like it should.


Regards, John McGraw