Just discovered my battery drain, which seems to be from the "on" wire that feeds to the alternator. With key-off, the wire is still showing 12v+? Is that wire supposed to be key-on 12v? I only have 2 wires (not including the actual charge wire), this one and the dummy light source. I swapped in an ez36 alt, which has the 3 wire, plug.

 

Anyhow, is there an easy place to convert the wire off a key-on source under the hood? Ideally from the underhood fuse box? i.e. bypass the factory wire and run my own key-on wire.

After reading some other threads, it was mentioned the newer Subaru alternators kick on via rpm-based activation (many alternators are either/or),which is odd as I clearly remember checking it when during the initial retrofit, as it wouldn't charge until the wire was connected. However, after deep charging the battery and starting the car, it was definitely charging w/o the wire connected at idle. Gonna see if it can do w/o the wire.

That wire is supposed to have 12v at all times. It's the remote sense wire but in practice they just crimp it back into the main output from the lug on the alternator about 8" downstream of the alt.

 

The alt will charge without it - that's not the field flash. The dummy light circuit is the field flash. 

 

Yes they will self excite but you have to get the alt shaft speed to like 5,000 RPM for that to happen if you disconnect the field flash (dummy light) circuit. 

 

GD

Could you have a shorted diode causing the drain?   Look for AC on the output to check.

It's definitely self-exciting at idle and charging w/o the wire (any wire) attached. Just drove to appt. and it sat for an hour, and cranked strong, but showing a bit high running voltage of 15v when I know it was 14 in the past, unless the meter is wonky, which is entirely possible. Will have to check in the morning if it's low.

 

 

I'm unsure about the diode being bad. Just set to AC on multimeter and probe battery posts? 

Well, I've left the wire unattached, and so far it's charging w/o issues, and seemingly it's not being drained now and is cranking strong after sitting a couple days. And just to be clear so someone skimming doesn't read that wrong, the alternator is a 130 amp out of an 11' Tribecca with the EZ36.

that alt. probably had the Tribec's ECU controlling it's field - not sure, maybe GD can explain.

Yeah, I believe you are correct. Could have sworn it wouldn't charge w/o that wire tho after 1st installing, as I remember going through the effort to splice the connector.

 

However, had radio on for 1st time after pulling wire and one/both amplifiers are super noisy all of a sudden, as if a ground wire was bad and it wasn't able to suppress the alternator noise anymore. Gotta figure out if it's related or a ground is loose to one of the amps.

I would attach the "charge" light wire and leave other off.  Might control voltage better.

 

at any rate to track down the drain put an Ammeter between teh negative battery post and the Neg cable.  You will see the draw in amps or milliamps.  begin pulling fuses from the fuse box until the draw goes away.  Once you know which fused system has the draw you can begin testing by unplugging individual components.

 

If none of the fuses make a difference.  Then try disconnectiing hte Alt.  If that eliminates the draw there is at least a partial short in the ALT.

I think there was an issue getting the charge light to cooperate with the newer alt. IIRC, it wouldn't go out. Alt has been in the car roughly 3 years now. Thought faulty batteries were the initial issue, as the last 2 winters they died and I just replaced under warranty.

 

 

It's holding the charge, so I'm thinking it was the way it was connected. I checked, and no AC current, so diode is probably ok. Amplifier noise is something else apparently that decided to act up at the same time the draw became an issue.

 

I'll check it's draw eventually. Just glad it's drivable atm. Might be able to squeeze another year out of it before the rust becomes terminal