I just completed converting to a later model 90a Denso alternator on my '71 Dart, and I have a question. Please note this alternator was recently rebuilt by a local reputable alternator/starter specialty shop.

I connected the 10awg wire from the B+ output to the battery + to avoid overload since I haven't done anything to the stock ammeter. When I started the car the needle dropped decharging ever so slightly, still nearly in the middle and on the middle white line. When I turn on the lights or heater, it drops down a little more, maybe slightly below the line. The needle sits there if i'm driving too.

This sorta freaked me out....I thought maybe my battery wasn't charging, but to test I dropped the idle pretty low with lots of things turned on, and I saw the lights dim until I brought the engine back to normal idle. I've also driven the car for several days, everything seems fine, so I assume this is normal? I'm aware that the ammeter will no longer show charging with my 10awg bypass wire in place, but I'm just wanting to confirm the way the needle is acting now is correct.

Mine does the same thing. The current is flowing the new path of least resistance. You can check the voltage with a voltage tester to be sure.

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11.02 @ 120.56
http://www.youtube.com/watch?v=EAxRmoDgsdY
Chassis dyno
http://www.youtube.com/watch?v=wd6hFGzLJMc

Yup, you need to disregard the ammeter; it won't tell you anything accurate now.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Same thing happened when I did this to my Satellite. Nothing to worry about.