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-   -   Alternator question, battery is discharging quickly. (

FC Zach 02-23-2017 08:26 AM

Alternator question, battery is discharging quickly.
For a while until this Monday, I have been dealing with some mystery drain to my battery. I found it by accident while detailing the engine bay where I heard a faint electrical whine that seemed to come from the alternator which stopped after removing the battery lead.

Before finding this issue, I'd have to keep a trickle charger connected to the battery or else it would completely drain within a couple weeks. It was attached when I found this problem. I left the lead off the alternator and disconnected the charger and left alone for a few days.

After giving it a few days with the charger and alternator disconnected, I reattached the charger to see if it would attempt charging the battery but it didn't. It was fully charged so I can confidently say it was the alternator.

-'87 RX7
-3rd Gen Alternator
-The 2 pin connection on the alternator is vacant
-Battery is good, tested. Tried another in case.

My questions:
-Does the two pin connector need to be connected to the alternator?
-If it's not a bad alternator (going to test it soon), any recommendations on what to check next?

djmtsu 02-23-2017 08:32 AM

One of the pins on the alternator needs to be connected.


FC Zach 02-23-2017 08:42 AM

It used to be connected. . When researching about it years ago I was under the impression that it was a redundant connection. So. . some time ago, about the time I converted it to EFI, I removed that connector to clean things up.

Since it's been a while since I've done this, I do not remember where that wire goes. Is it switched or constant 12v?

FC Zach 02-23-2017 08:45 AM

With that being said and before it's mentioned. . I never made the connection of the two because I thought the drain was related to the Haltec wiring and not this little single wire connection.

djmtsu 02-23-2017 08:45 AM

I believe switched. The main power wire is of course constant.

FC Zach 02-23-2017 08:51 AM

Sweet. . but what change would it have in my case if that connection is switched 12v?

FC Zach 02-23-2017 09:05 AM

When I connect the bottom pin to the battery lead on the alternator, the whine goes away.

TitaniumTT 02-23-2017 09:06 AM

One of the pins needs to be connected to the battery, or a constant 12v+ source. The other pin pulls current through the idiot light. If both of these aren't connected, it will drain.

If you only have ONE wire run to the Alternator, you can use a resistor to mimic the difference in current at the alternator.

FC Zach 02-23-2017 09:19 AM

Could I simply do this, connect here?

TitaniumTT 02-23-2017 09:20 AM

Sounds like the bottom pin goes to the battery, the top pin goes through the idiot light.... oh, that pin needs to be keyed as well

FC Zach 02-23-2017 09:20 AM

I've never had the top wire (the empty spot in the connector) connected to anything. Is that recommended?

TitaniumTT 02-23-2017 09:21 AM


Originally Posted by FC Zach (Post 339856)
Could I simply do this, connect here?]

You could, and you could use a resistor to connect to the top pin, however the top pin needs to be keyed or you'll get the same drain

TitaniumTT 02-23-2017 09:22 AM


Originally Posted by FC Zach (Post 339858)
I've never had the top wire (the empty spot in the connector) connected to anything. Is that recommended?

It's necessary to keep the alt from draining the battery, unless you do a complete battery disco, which I usually do anyway because Rotary.

FC Zach 02-23-2017 09:33 AM

Ok cool, thanks guys!

One problem though. . I don't remember but does this connector have the "idiot light" wire you speak of?

TitaniumTT 02-23-2017 09:37 AM

Yes, one wire is straight to the battery, the other pulls through the idiot light.

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