alternator question
Senior User
Joined: Oct 2005
Posts: 145
Likes: 0
From: ventura, CA
Well what your Haynes manual says would be true only if you have no accessories that are powered with the key off. Your clock and radio both are taking power even with the key removed so it is normal that you are getting 12V with the terminal removed and measuring between the terminal and the battery.
My post assumed your battery terminal was always installed on the battery - my check tells you if you have a bad cable due to excessive voltage drop.
My post assumed your battery terminal was always installed on the battery - my check tells you if you have a bad cable due to excessive voltage drop.
More Turbo
Joined: Aug 2004
Posts: 689
Likes: 6
From: Rodeo, Ca.
That means you have a current draw somewhere, put an ammeter in & see how much. Also unhook the hot wire from the alternator, if it has a bad diode you'll have current drain there, (the diodes prevent backflow of the current).
Cargo Master
Joined: May 2001
Posts: 3,208
Likes: 13
The test I run is to take the postive terminal loose and use a low voltage test light between the battery post and the cable end. If it lights there is a drain that will run down the battery. IF it doesn't then everything is fine. On todays computer controlled vehicles there is always a small current draw for the keep alive circuit in the computer plus the digital clock. Just make sure all doors are closed and the hood light if equipped is disabled. The alternator voltage when running should be between 13.5 and 15 volts with 14.0-14.5 being usual. I have found alternators that would draw current when they where not turning but would charge when running this is caused by a bad diode. When I work on one with a current draw when it shouldn't I start by disconnecting the alternator first and then start pulling fuses until I find the culprit circuit and then chase out the componet from there. The number one offender I have found is the glove box light staying on.
