Ok been having a problem where my alternator has this humming sound when car is off. Been doing lots of research and basically my alternator is getting power somehow when car is off. Went out to look at wires today and saw that I have the thick red wire on back of the alternator going to battery (good) then the plug in connector on the bottom of the alternator has three wires coming from it, a tan wire, a brown wire and a thicker red wire. I followed the thicker red wire and it wasn't connected to anything. Has a connector on it where it looks like it's supposed to hook to the starter solenoid. I've been driving with that wire disconnected for weeks now and the alternator charges fine with car on(lights on and everything as I do 95% nighttime driving) I do disconnect the battery overnight as the alternator will have a whine if I don't and I fear I will have a dead battery in the morning. So what does the medium thick red wire coming from the alternator to starter do?

 

Sorry car is a 88 firebird tbi converted to hei carb setup

 

That red wire is the voltage sense wire from the alternator which helps with maintaining the system voltage level. The alternator will try to maintain approximately 13.7 volts at that wire and will adjust it's output to achieve that voltage at that wire. Most diagrams show that wire going to the solenoid or the power distribution block through a fusible link. HTH!

 

Ok thanks got it hooked up now, couldn't figure out why the alternator was getting voltage when car off so I just wired in a switch for alternator now it's good to go.