Hi guys, new here and have an issue with a 91 f150 5.7. Long story short... Battery light came on, changed the alternator, battery light came on again, changed the alternator again, recharged the battery, light went off, driving the car died, dead battery, new battery. Battery light goes on when at idle, goes off when you accelerate. Is it possible that there are 3 bad alternators? Changed the ground wire also from the battery. The thing is, the battery doesn't charge when the battery light goes off so it's running directly from the battery. Any advice? Thanks in advance!

 

have to figure which wire triggers the alt. and make sure its getting 12 volts when running. it may not be getting turned on to start the charging. changed my alt many years ago, but there has to be 12 volts being sent to it when the engine is running to trigger the alt to charge.

 

Has the pigtail connection that hooks onto your alternator been changed? If not that could very well be your problem. There is a pigtail connector available, that you cut your old connectors off and solder(recommended over crimp connections) in place.