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Old 09-17-2016, 08:02 PM   #1
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Default Help with power draw after FD alternator swap

I have an FD alternator swapped into my 1999 10AE. It was swapped in using this method-- http://www.miataturbo.net/general-miata-chat-9/how-nb-na-alternator-swap-45950/#post650352

Ive had troubles with the battery going dead while sitting since I bought it a little over a year ago. The battery checked out bad, so I replaced it a month ago and the problem seemed like it was gone for a few weeks. Now the new battery is dead also. I have a jump box hooked up in the car as the battery while I started hunting for the draw, will get the battery warrantied after the draw is cured. Testing showed I had an approximately 0.30 amp draw.

After hunting around and pulling fuses for a little bit I discovered that the draw seems to be coming from the 12v switched source hooked to ecu connector wire 1o (gray/red). When I pull the fuse the draw drops down to 0.01 - 0.03A. I tried moving it to a different 10a switched source in the fuse box and the draw is still present.

Does anyone have any ideas of how to eliminate the draw? Any chance it's from a defective alternator? Or is something wired wrong?
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Old 09-17-2016, 08:34 PM   #2
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How is it drawing power if it is a switched source...doesn't that mean it isn't connected to 12v when the key isn't on.
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Old 09-17-2016, 09:25 PM   #3
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I have no idea how its happening, the grey/red wire hooked to the 12v switched seems to be the problem though. It's on a fuse buddy in the wiper fuse, also tested in the radio fuse, still creating a draw in both.

As for further testing I've done, with the fuse buddy plugged in and creating a draw the alternator outputs 14.2 volts with all loads off and 14.1 with high beams and blower motor on. Then I left it connected this way and disconnected the alternator connector. The draw disappeared when the connector was disconnected and the alternator output changed to 14.8 with no load and 14.7 with loads on.
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Old 09-17-2016, 09:31 PM   #4
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If it's drawing when off maybe it's not a switched source?

Because by definition a switched source can't draw power when off...
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Old 09-19-2016, 04:01 PM   #5
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Got a chance to do a little more testing today.

According to the voltmeter there is no power going through either of the switched 12v sources I tried (radio and wiper fuse). The draw is still present though. This is leading me to think that maybe the alternator is back feeding the power to it somehow.

So now I can either wait 10 days for a replacement alternator to come in so I can try swapping those and see if the problem persists or try wiring in a relay to feed it power.
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Old 09-26-2016, 04:25 PM   #6
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Dropped the car with my mechanic friend who has a turbo II rx7 running the FD alternator over the weekend. He checked how it works on his and compared to mine. On his car, the alternator plug wire that is in the same location as the gray/red wire in mine was connected to a 12v constant source. He switched mine over to a 12v constant source as well and now the draw is gone and charging is back to 14.1v unloaded and 14.2v loaded.
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Old 09-26-2016, 09:30 PM   #7
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put the nb alternator back in
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Old 09-26-2016, 09:54 PM   #8
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Quote:
Originally Posted by bjorno View Post
put the nb alternator back in
Nominated for worst comment in the world
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