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I'm having a problem with my alt charging my battery. After multiple alt and battery replacements, I've narrowed it down to the exciter circuit not signalling.
12V is present at the 2 outer wires of the 3 pin connector but never at the center red when key is on. My understanding is that this is fed through the charge light circuit, which won't illuminate. After tearing the dash apart I found 12V at the charge bulb but no light. Switched with a known working one from blinker and still no go. How is this possible with battery voltage present?
Anyone ever have issues with these speedos shorting out. Any help will be appreciated. Thanks
The red wire (IG, pin 2) should have battery voltage through the Engine fuse with key-on. This does NOT go through the "ALT light" circuit. That's the Yellow wire (L, pin 1), which should be at ground when the alternator is not turning. (For completeness, the white wire, S ("sense") is at battery voltage ALL the time.)
There is, of course, battery voltage at the "alt light" bulb with key-on. When the alternator is not turning, the L (yellow) wire is at ground, so current flows through the bulb, illuminating it. Once the alternator starts generating power, the L wire rises to about 14.1 volts (as does the battery). With the same voltage on either side of the bulb, the alt light goes out.
Start by disconnecting the connector from the alternator. With your voltmeter to ground, you should have battery voltage on S (white) all the time. You should have battery voltage on IG (red) with key on. With the connector out, you will also get battery voltage (through the Alt light) on L (yellow). If you don't have battery voltage on the red wire (pin 2), you have a wiring problem (or maybe only a blown Engine fuse.)
Last edited by scope103; Feb 28, 2019 at 07:46 PM.
The red wire (IG, pin 2) should have battery voltage through the Engine fuse with key-on. This does NOT go through the "ALT light" circuit. That's the Yellow wire (L, pin 1), which should be at ground when the alternator is not turning. (For completeness, the white wire, S ("sense") is at battery voltage ALL the time.)
There is, of course, battery voltage at the "alt light" bulb with key-on. When the alternator is not turning, the L (yellow) wire is at ground, so current flows through the bulb, illuminating it. Once the alternator starts generating power, the L wire rises to about 14.1 volts (as does the battery). With the same voltage on either side of the bulb, the alt light goes out.
Start by disconnecting the connector from the alternator. With your voltmeter to ground, you should have battery voltage on S (white) all the time. You should have battery voltage on IG (red) with key on. With the connector out, you will also get battery voltage (through the Alt light) on L (yellow). If you don't have battery voltage on the red wire (pin 2), you have a wiring problem (or maybe only a blown Engine fuse.)
Thanks for the quick reply.
Where does the voltage that illumates the charge bulb come from. And what correlation does it have to the red exciter wire. I find it odd that 12V being at the bulb and it not illuminating and 12V not reaching the exciter ciruit have nothing to do with the each other.
Last edited by yota tay; Feb 28, 2019 at 08:41 PM.
The battery voltage on the alt light is from IG2 through the IGN fuse. The battery voltage on the IG (red) wire is from IG1 through the ENGINE fuse. The reason your ALT light is not lighting (if it has battery voltage on one side) is because you DON'T have ground on the other side. That ground is supposed to be through the yellow wire to L. So it sounds like you have a wiring problem.
But as I said, your multimeter will give you the answer.
The battery voltage on the alt light is from IG2 through the IGN fuse. The battery voltage on the IG (red) wire is from IG1 through the ENGINE fuse. The reason your ALT light is not lighting (if it has battery voltage on one side) is because you DON'T have ground on the other side. That ground is supposed to be through the yellow wire to L. So it sounds like you have a wiring problem.
But as I said, your multimeter will give you the answer.
Thank you much sir. That yellow wire must be the common in this circuit.
As Scope says^^^...
Correct. The charging circuit will work even without the "L" wire connected.
(Excitation through charge fault light belongs on the GM system - which is not reliable - what if charge light bulb burns out?)
O.P.,
Please put everything back to stock and do voltage checks as Scope says above.
[QUoOTE=RAD4Runner;52419542]...Thanks for the diagram. My issue has to be at the turn hazard switch...
If you're not getting 12V on red IG wire at alternator connector, AND also having issue with TURN signal but BUT NOT hazards, most likely issue is Engine Fuse circuit.
Toyota did not have the most brilliant electrical* engineers back in those days.
They named the fuse "Charge" fuse when it did not power the charging circuit.
They took power for the "TURN" signals, the backup lights - that you can remove completely and not affect engine function - , etc from the engine fuse. DUH!
*Toyota definitely had much better mechanical engineers than electrical engineers back then.
If you're not getting 12V on red IG wire at alternator connector, AND also having issue with TURN signal but BUT NOT hazards, most likely issue is Engine Fuse circuit.
Toyota did not have the most brilliant electrical* engineers back in those days.
They named the fuse "Charge" fuse when it did not power the charging circuit.
They took power for the "TURN" signals, the backup lights - that you can remove completely and not affect engine function - , etc from the engine fuse. DUH!
*Toyota definitely had much better mechanical engineers than electrical engineers back then.
Before my alt quit the first time I was having a turn signal/ overdrive issue that was blowing the 15 amp fuse. Removed flasher relay and reinstalled and fuse never blew after that. Now it seems that something in that area is malfunctioning messing with the red wire signal. Will probably replace the whole wire.
Please always indicate what you're working on (See signature)
Originally Posted by yota tay
Before my alt quit the first time I was having a turn signal/ overdrive issue that was blowing the 15 amp fuse. Removed flasher relay and reinstalled and fuse never blew after that. Now it seems that something in that area is malfunctioning messing with the red wire signal. Will probably replace the whole wire.
No need to replace wire Just thoroughly inspect all wiring after engine fuse (R, G-L, etc) for shorts to ground.
I think Yota Tay is driving a '94 (yes, Rad4Runner already asked him to put his vehicle info in his signature). My EWD for a '94 shows the backup lights powered from the CIG fuse (tail lights on the TAIL fuse, turn signals on the TURN fuse). The ENGINE fuse powers the IG terminal (red wire) of the alternator, and the Cruise ECU (I didn't see anything else on the ENGINE fuse, but someone may know better).
In other words, we're all wasting our time until Yota Tay puts his multimeter to ground on the tabs on top of his ENGINE fuse. If that's blown, I wouldn't expect the alternator to work. (and I would check that fuse and circuit long before I replaced a battery or alternator, but that's just me. And anyone following the FSM.)
I think Yota Tay is driving a '94 (yes, Rad4Runner already asked him to put his vehicle info in his signature). My EWD for a '94 shows the backup lights powered from the CIG fuse (tail lights on the TAIL fuse, turn signals on the TURN fuse). The ENGINE fuse powers the IG terminal (red wire) of the alternator, and the Cruise ECU (I didn't see anything else on the ENGINE fuse, but someone may know better).
In other words, we're all wasting our time until Yota Tay puts his multimeter to ground on the tabs on top of his ENGINE fuse. If that's blown, I wouldn't expect the alternator to work. (and I would check that fuse and circuit long before I replaced a battery or alternator, but that's just me. And anyone following the FSM.)
The fuse is good with 12V present and passing thru. It's just not making it to the alternator. I'm going to trace that wire and repair or replace. The diagram was all I needed. Thanks
My diagram is for 1986-1988 22RE. Not sure if exactly same as yours when it comes to the fuses part.
It's the same as far as the red wire. Anyhow that was all I needed to make repair. Thank you very much.Traced red from alternator up the wiring loom to 4 prong molex to fuse panel. I wished someone would have mentioned the plug at the fuse that excites the alternator, I would have started there and it would have made troubleshooting way easier. The wire was bad right at that connector.
...I wished someone would have mentioned the plug at the fuse that excites the alternator, I would have started there and it would have made troubleshooting way easier. The wire was bad right at that connector.
No one knows exactly at which point wiring fails. Apparently no one else has had that red wire fail at that connector.
The key to effective troubleshooting is to understand how the system works. What is it supposed to do, what it is not doing, then figure out why it is not doing it.
Last edited by RAD4Runner; Mar 4, 2019 at 12:09 PM.
Exciter charge?
Start by disconnecting the connector from the alternator. With your voltmeter to ground, you should have battery voltage on S (white) all the time. You should have battery voltage on IG (red) with key on. With the connector out, you will also get battery voltage (through the Alt light) on L (yellow). If you don't have battery voltage on the red wire (pin 2), you have a wiring problem (or maybe only a blown Engine fuse.)
I disconnect the plastic connector, and my voltmeter reads +12v for all 3 of the wires. The red battery icon is light in the dashboard with engine off. When everything is connected, if I start engine - the red battery icon on dashboard is light with the engine running.
(whoopse), sorry - I replied to the wrong thread here - I do not have a "DELETE button just an "EDIT" button, so now this reply is stuck here.
Last edited by Erich Stein; Mar 15, 2019 at 07:44 AM.
Reason: Posted reply on wrong thread
Feb 28, 2019 | 06:38 PM
