The alternator is NOT a permanent magnet alternator. The sensing wire is what magnetizes the alternator. Touch the alternator pulley with the tip of a screwdriver with the key in the RUN position.
If you feel the magnetic attraction the alt. should be good. Back, again, to the alt to battery circuit.
A guy at work asked if he should file for divorce . . . I told him he’d best talk to a professional marriage counselor 
I’ve never met the guy’s wife, so I literally have no opinion about the matter
Mr Wizard, as in the '60s cartoon: [ https://www.youtube.com/watch?v=ZuvQRdDJtLA
](https://www.youtube.com/watch?v=ZuvQRdDJtLA)
I apologized for not being clear. End Trans.
Remember the schematic ‘tester’ provided? It shows that the ‘s’ (sense line) is always connected to the battery. The ‘s’ line sends the battery test voltage to the Zener diode that turns ‘on’ the transistor that turns ‘off’ the driver transistor that deenergizes the field ‘alternator rotor’. With the rotor ‘on’, the stator produces AC that is rectified thus charging the battery. When the battery voltage gets high enough the field gets turned ‘off’.
With the stator producing AC why is the diode trio not producing voltage; carrying terminal ‘l’ to high voltage; matching the battery voltage; and turning the ‘charge’ light off? because ‘l’ wiring is shorted to ground.
On the schematic that ‘tester’ provided the Sense Line (S) goes directly to the Alt-S fuse. From the Alt-S fuse it goes through the Fusible Link to the Positive Terminal on the battery. The schematic shows the Sense Line DOES NOT go through the ignition. My question from several posts back was if I, or the auto electric mechanic, puts a line with a 5 amp fuse from the positive battery to the sense line would it fix the issue. Looking at the schematic it should. At this point I’m not planning on doing this but I will ask the auto electric mechanic how much will it cost to do this and see what he says.
When Couger said “When you saw .2 volts (on the sense line) without the fuse in place you were reading some back feed voltage from the regulator and wasn’t a concern” isn’t true. This is because I had the wiring harness with the sense line removed from the alternator when testing so there would be no back feed voltage from the regulator. It would just be a line connected to the removed Alt-S fuse slot and should of had no voltage. This leads me to believe this line is shorted with something.
Where can I find the actual wiring diagram for a 2004 Toyota Corolla Matrix? The one posted appears to be for a 2004 Toyota Sienna. Maybe it’s the same but I’m sure.
Stop futzing around with the Sense line. Your problem still remains that the alternator is turning ‘on’ without power to the regulator/field circuit. Without power to the regulator how can the Sense line work. Since the stator is obviously working (overvoltage) why doesn’t the diode trio develop voltage from the stator AC; power the regulator; bring the Lamp line up to alternator output voltage i.e. battery voltage; and put 0 volt drop across the idiot lamp? Because the Lamp line is shorted Remove that connector from the plug or cut that line and see what happens
“You can lead a horse to water but you cannot make it drink”
OVER AND OUT
That wire now has no real termination and becomes a good antenna for induced current. 0.2 volts means nothing. That’s a red herring…
If the schematic above matches the way your car is actually wired – the battery + is wired directly to the “S” alternator terminal through just one fuse – do you find that measurement result a little unusual?
Several options
Now I now better than to just start replacing things like the battery and alternator when the battery light is on. I think my battery was damaged from over charging when my alt was putting out 16.3 volts so I did need it replaced but the alternator was fine.
The cause turned out to be the sense wire was breaking and probably down to the last couple of strands of wire. Due to this there was resistance in the sense wire causing the voltage to show erratic voltages like 5v or 7v to the regulator. In turn the regulator thinking the battery is extremely low started putting out 16 plus volts to charge the battery. The 16 volts caused the water in the battery to boil and become low causing damage to the battery. Yikes, such an unusual problem. I found removing the Alt-S (alternator sense wire) fuse I could drive the car and the alternator would put out a continuous voltage around 14.3 volts. I believe this is because when no voltage is on the sense wire the regulator defaults to putting out the 14.3 volts.
Anyways, I put in a new sense wire and all is good. The sense wire is a direct wire from the alternator to the plus battery terminal (with a fuse). I was going to take it in and have a mechanic do it but it’s amazing how few mechanics will do anything electrical. One place I went to known for fixing electrical issues on cars wanted to charge me $480 to put in the wire after I already had diagnosed the issue. I guess they want the money for diagnosing not just the money for doing the repair. I spent $30 or so on wire, tubing, tape, a fuse holder and zip ties and fixed it in a couple of hours. All the parts I bought were high temp and fire resistant rated.
I got the information on how to trouble shoot the issue from the toll free number for Carquest parts. I appreciate the support they gave. They had me take off the three wire harness from the alternator turn the ignition to on but not start the car. Then I measured the voltages from all three of the wires on the harness. All of the wires should show around 12 volts. If any of the wires don’t show around 12 volts there’s an issue. In my case the sense wire was not showing 12 volts and when I checked it at different times it showed different voltages all less than 12 volts.
On the 2004 Toyota Corolla Matrix (yes Corolla, it’s a different body but same engine for this year) the pin-outs on the wire harness connected to the alternator are:
1 Yellow wire – For the warning light circuit – On with ignition
2 Red with white tracer wire – Power wire for the regulator – On with ignition
3 White wire – Sense wire, direct connection to positive battery – always connected
My issue was the sense wire. If the Power wire for regulator is off or low voltage the regulator might work erratically. If the Warning light wire doesn’t show 12 volts, most likely the battery light won’t be on. When there are charging issues the regulator will switch the connection to the warning light wire (yellow wire) to ground which completes the circuit to turn on the battery warning light.
I hope this advice may help someone in the future.
Thanks,
B7
Good for you. Glad you are back on the road with a proper charging system.
A shop tech would be unwise to simply replace a wire the customer specifies without doing a full diagnostic procedure first . The reason is that they might be liable for any adverse consequences.