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Senior Member
Alternator wiring when using standalone ECU
So I am using a standalone ECU and when I run the engine the alternator is not charging the battery. I am wondering if I need to do something with the wire from the alternator that used to go to the charge light on the dash. Since I am not using the Subaru ECU I assumed I did not need it. Does that wire have an effect on the alternator's function or is it only for the factory ECU's use?
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I've heard that occurs when the odometer is unplugged to prevent racking up miles on the car without them being recorded.
I don't know for sure that's your issue, or how to fix it, but might be a start. I'm sure somebody has figured out what signal that wire is looking for to engage the charging circuit. You do definitely need that wire connected to something.
Last edited by phil1734; 12-01-2017 at 02:30 PM.
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Yes, I love Technology
Pretty sure Subaru alternators use the same setup as pretty much all the rest. Typically the charge light circuit provides the initial trickle current to start the magnetic field up in the alternator. If it is disconnected, the field can't build = no output. Sometimes an alternator has enough residual magnetic field to get going but that old timer's claim may be a wives tale, not sure.
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Administrator
On the plug, apply battery voltage to the blue/red wire and switched voltage to the black/white wire through the alternator light in the gauge cluster.
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Senior Member
Originally Posted by
Wayne Presley
On the plug, apply battery voltage to the blue/red wire and switched voltage to the black/white wire through the alternator light in the gauge cluster.
I am not using a Subaru dash, so no light to connect through. Can I just connect it to 12V switched voltage or does there need to be some current draw in the circuit?
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Senior Member
No, You need a light bulb or resistor in the circuit.
Here is a nice discussion on alternator warning lamps.
http://www.lotuselan.net/forums/elan...tc-t10387.html
They refer to the bulb being 2 watt 12 volt.
so if you want to put a resistor in that line instead.
V^2 / P = R ------> 12^2 / 2 = 72 ohms
So I would something around 72 ohms + or - 10.
You need 2 watts.
I don't like things that get hot, so I would use at least a 10 watt resistor.
Bob
Last edited by Bob_n_Cincy; 12-02-2017 at 12:24 AM.
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Senior Member
Thanks Bob, you the man I'll try that this weekend.
Although, once the alternator self excites and the voltage on both sides of the resistor are equal, there would no longer be any current flowing and hence no heat right? So the resistor does not need to be so beefy as its only has current flowing for a brief moment until the alternator self excites right?
Last edited by Hobby Racer; 12-02-2017 at 08:09 AM.
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Senior Member
Originally Posted by
Hobby Racer
Thanks Bob, you the man
I'll try that this weekend.
Although, once the alternator self excites and the voltage on both sides of the resistor are equal, there would no longer be any current flowing and hence no heat right? So the resistor does not need to be so beefy as its only has current flowing for a brief moment until the alternator self excites right?
Yes, BUT
if you have an alternator failure, belt failure, or just forget to turn off the key. the resistor or light stays on.
Bob
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Senior Member
Originally Posted by
Bob_n_Cincy
Yes, BUT
if you have an alternator failure, belt failure, or just forget to turn off the key. the resistor or light stays on.
Bob
Good point. better safe than on fire.
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