Alternator works intermittently, what's up with the blue wire? Just when I think I need to order an alternator it starts working. I disconnected the little blue wire started the engine and after a minute the battery light came on and of course it was not charging the battery. But when I had to move it I plugged the blue wire back in and the light never came back on and it was kicking out 14v. So I took it down the road for quite a few miles before I came back and it still never came on. With all the different variables for the alternator / generator to work I can't get an accurate reading for because of this or because of that. what is a definitive test?

 

I would say your alternator is OK. The blue wire is for the field and is controlled by the ECU. It sounds like you need to do a really good cleaning of the connector. Use a grease and corrosion cleaner. They do the job differently and one will not fix the other problem.

 

Can't hurt to check and clean all of the alternator connectors, including big wires. And engine grounds.

But unless you're in a high corrosion area, modern connectors usually don't get gunked up.

It's still possible that the alternator is just failing, that's common enough.