Toyota 5FGC25:
Alternator Wiring Diagram?

There is a 3 wire plug on the alternator, I assume one goes to the lamp in the dash, one goes to battery positive, and the other goes to the run position on the key switch? On the truck in question, it has been killing batteries and alternators. When I got to the truck, the battery was boiled dry, at only 10.2V, and the alternator was drawing 160ma of current with the truck off. After looking over the wiring, which is an absolute mess from several hack technicians working on it, I found an odd wiring arrangement. One wire goes to the dash, another to a 10Amp fuseable link to the battery, and the third goes through half a dozen butt splices and ends up at the battery positive terminal. Seems to me like that wire should be going to the keyswitch. Could this wiring arrangement be causing battery drain, which in turn causes the alternator to increase its field current, in turn putting out a higher charge to the battery, thus boiling it dry and straining and eventually killing the alternator? Or am I way off base here?
  • Posted 2 Jun 2012 09:11
  • Modified 2 Jun 2012 09:12 by poster
  • Discussion started by yaleford
  • Ohio, United States
Showing items 1 - 3 of 3 results.
Ok, I will correct the wiring when I return. Thanks guys. As for the email address thing, does this forum not do the Private Messages? This is a VERY strange format forum for me, I have never seen one set up so stone-age like this. It's a bit tough to navigate.
  • Posted 2 Jun 2012 21:08
  • Reply by yaleford
  • Ohio, United States
I think all your assumtions are correct. L goes to lamp on dash, S goes to the 5A fuse in the box that is hot all the time, IG goes to the 7.5A fuse in the box that turns hot when the key switch is on.
  • Posted 2 Jun 2012 12:12
  • Reply by mrfixit
  • New York, United States
do you have a email address to post in your profile,in case anyone had any info for you....
  • Posted 2 Jun 2012 09:43
  • Reply by kevin_t
  • Pennsylvania, United States

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