bad alternator??
Administrator
Joined: Apr 2010
Posts: 87,411
Likes: 4,214
From: Clayton MI
A couple of weeks ago truck wouldn't start. Battery was dead. Threw in a new battery and it started. The next morning the new battery was dead (overhead map light switch). Jumped it, let it charge a few from the other car, then took the negative cable off and truck died. Onto a new alternator. Usually on older vehicles when the battery dies the alternator isn't too far behind or vice versa.
Veteran
Joined: Jul 2013
Posts: 338
Likes: 55
From: TN
A couple of weeks ago truck wouldn't start. Battery was dead. Threw in a new battery and it started. The next morning the new battery was dead (overhead map light switch). Jumped it, let it charge a few from the other car, then took the negative cable off and truck died. Onto a new alternator. Usually on older vehicles when the battery dies the alternator isn't too far behind or vice versa.
Grand Champion
Joined: May 2019
Posts: 5,147
Likes: 721
From: S.W. Indiana
Disconnecting the battery while running is a simple way to destroy ANY alternator equipped system. Not only will it freak a computer out, pre-computer cars from the early 1960's and up have alternators. Unlike generators, which you CAN disconnect, there are NO permanent magnets in an alternator. There IS a diode. It's a little bitty thing but critical to the alternator working. Unhooking the battery while running is like cross jumping a battery. It can blow that diode out right away. You now have no way to change the AC the alternator makes to the DC current it needs.
Veteran
Joined: Jul 2013
Posts: 338
Likes: 55
From: TN
Disconnecting the battery while running is a simple way to destroy ANY alternator equipped system. Not only will it freak a computer out, pre-computer cars from the early 1960's and up have alternators. Unlike generators, which you CAN disconnect, there are NO permanent magnets in an alternator. There IS a diode. It's a little bitty thing but critical to the alternator working. Unhooking the battery while running is like cross jumping a battery. It can blow that diode out right away. You now have no way to change the AC the alternator makes to the DC current it needs.