Alternator wiring problem?
 

OK so searches all over the internet have not landed me a solution.

yes I have the FSM. yes I have been using it.

Basically my car destroys alternators in literally seconds.
87 FC turbo 2 car with an S4 NA engine in it.

car ran decent until i let it sit for a few weeks and had to jump start it. alternator died right there. (I found out up the street when the battery couldn't keep the engine running any more.)

New alternator. drives good for a day. don't drive it for a few days, jump start again. Immediatly getting voltage off the charts, 16-17volts, so I shut her down before anything blows up (obviously a bad regulator and now I assume a bad battery). take the alternator and the battery in to get tested both fail miserably.

New battery. New Alternator. thank jeebus I get deals on them.
fire it up. runs fine but I immediately notice the voltage gauge sitting at 12voltsish give it a rev, no change.
hit the Alternator and the battery with the multimeter obviously the alternator is not charging and after another test this one is toast. battery is still good though.
total run time maybe 3 minutes at idle

So I figure I have a short or a bad ground or a ground I shouldn't have.
I checked the grounds based on this information Proper RX-7 Grounding Procedures


Now I grab my multimeter again and using various sources. particularly this picture
Attachment 667599



I find that with the key on all three alternator connections show battery voltage, like they are supposed to? Correct me if I'm wrong.

with the key off and the battery unhooked I start poking around with my meter and what I find that I didn't expect is that the Black/white stripe (ign switch) wire from the back of the alternator has continuity to ground.

now I may be mistaken but I believe that wire leads to the 15amp Engine fuse in the interior fuse box. just for kicks I checked that out and it has continuity to ground on both side of the fuse with it removed.

I thought that none of the alternator wires should have continuity to ground especially with the key off and the battery unhooked. Nobody told me that specifically I just thought that how things work. again correct me if I'm wrong on any of this.

at this point I basically need to know if that wire should have continuity to ground or not so I can move forward with trouble shooting elsewhere (short somewhere?) or if this is my problemo.

So if any of you grand wiring masters know if that is normal or not or if that might be my problem or not. or what might actually be my problem. Maybe someone can check their car and see if we get the same results.

Thank you very much. :icon_tup:

The B/W wire should have 12 volts w/key to on whether the plug is connected to the alternator or not. The W/B wire has a ground w/key to on and plugged into the alternator, but would show 12 volts w/key to on if the plug was disconnected from the alternator.

Yea i have all that but is that black/white supposed to have continuity to ground with the key off unplugged?

I'm not sure, but I'm also not sure it is relevant because if it behaves as it should w/key to on then it cannot accidentally be grounded out. And where are you sourcing the alternators from as a number of stores will have units which will not work from the get go and thusly have to be returned. Napa usually stocks alternators of value. And have you checked the alternator belt tension in addition to making sure it is lined up properly w/the pulley?

So I found someone else with an rx7 and tested his and his does not have continuity to ground like mine does so i am going to try and figure that out before trying anything else.