electrical gurus, please help explain this circuit (1 Viewer)

[emac]

@Coolerman , @Pin_Head @Poser and others wondering if you guys could help me understand the charge circuit on my 62.

The charge light, brake light and A/T temp light are all illuminated on the dash. My alternator is brand new. All fuses are good, and I get 14V at the battery when running. I am thinking there is something wrong with the cheap alternator I bought, and I have ordered a reman from Toyota. In the meantime I have been trying to understand the wiring diagram.

I am trying to understand how the "Charge light relay" works. Top right of diagram in first link. I can see how the three lights are connected, but I dont understand how electricity flows to make the light come on. I just dont understand the relay. I tested it from the WSM and it tested good.

https://www.ih8mud.com/tech/88lc-wire/88lc-wd4.gif

This link is for the alternator:

https://www.ih8mud.com/tech/88lc-wire/88lc-wd1.gif

I spent an hour searching for the right diagrams, and when I found them, I realize I am not smart enough to figure them out!

Thank you!

 

[OSS]

Those un related indicator lights all share a common ground behind the dash. I'd check that first. Although it might not be the problem, it should be ruled out.
Whenever unrelated indicator lights start lighting up inappropriately on the dash, the primary suspect is a bad ground- creating a floating ground. Electricity is flowing through a different path to ground (via the indicators) than intended.

This link below shows the grounding connector on a FJ60, but the FJ62 has one behind the instrument panel as well.

Is my alternator about to eat dust?

 

[emac]

Thank you for the reply @OSS. I agree it seems like a ground issue. I am planning to check the ground when I remove the dashpad. There is supposed to be one common ground that has been known to give trouble. The lights were not lit until after I replaced the alternator, and did not light up until it was driven for a while. Weird. They are on full, no flickering at all. Like a dead short. The old alternator wasnt charging, as i was only getting 12v at the battery. The store checked the alternator and said it was bad. Why the light was not on originally I cant answer as I just got the rig. I do know the previous owner had charging issues based on the receipts. So, it very well may be another issue (wiring).Unfortunately, the store has already sent back my old alternator. I really wanted to have it rebuilt, but the closest place is an hour away. Every thread I read on the 60's forum that had all the lights on was corrected by replacing the alternator.

I am just trying to understand the wiring diagram to try and come up with a troubleshooting plan. That "charge light relay" has me confused. I dont understand how it works. It looks like it has a diode. The charge light has one as well. Wondering how the electrons are flowing.

 

[FJACS]

I’m not an auto electric expert, this could be completely incorrect (my wiring has only burned 2 cars to the ground )....but it looks to me like the items in the cluster from check engine down to seatbelt all share a common +12v supply. Some of these items have their own unique ground, while others- such as the charge lamp and brake lamp use a switched ground.

The charge lamp ground is switched by the relay. When the relay closes, the circuit is complete and the light illuminates. The diagram shows that the relay will also ground out the brake warning light and differential light illuminating them as well. It appears that the relay is signalled by the yellow/black wire from the alternator.

 

[emac]

Me either, but I haven't burned anything..........yet! So, when the yellow black wire gets power signals the relay to ground the light circuit, or does NO power to the yellow black wire cause the relay to go to ground? If I knew then I could test the yellow black wire for power. It seems power is either ON when it shouldnt be or OFF when it shouldnt be. It is supposed to come on when ignition is on and go off when running, so the alternator would be doing something to send that signal.

My logical guess is power from alt turns light OFF.

 

[FJACS]

My guess is it’s a “normally closed” relay. With no signal from the yellow/black the relay is closed and circuit is complete. When the engine is running and alternator is producing current the signal opens the relay and breaks the circuit (lamp out).

 

[red66toy]

Are the terminals on the plug that connects to the alternator ok? Any broken or loose connections? If you jiggle the wires from the alt, do the lights change? Since it only happened after you replaced the alt I would suspect something at the alt causing the problems unless it's just a big coincidence.

 

[Pin_Head]

If the problem is that the dash lights are on appropriately, then I agree: It is probably a “floating” ground that they share in common. You can find it by hooking a test probe to ground and probing around the dash panel grounds until you find the spot that makes the lights go off.

 

[LAMBCRUSHER]

have you checked the fusible links? also, the big ground connector under the dash...

 

[LAMBCRUSHER]

and yes, power from the alt turns the charge lamp OFF

 

[LAMBCRUSHER]

via the charge relay

 

[emac]

Got it figured out, I think. I called the alternator manufacturer. He had the wiring diagram. The yellow/white wire coming out of the alt (L terminal) is supposed to go to dead when the alternator is running. This turns the light off. My L terminal was hot all the time, so light was on even though it was charging. Black/yellow is ignition and feeds the charge relay and is hot with key on. He said there is a computer board in the alt that is probably bad. Moral of the story: Dont buy junk. When I get the OE remanufactured alt I will know for sure. I dont think I have a wiring issue, just a garbage issue.

 

[Pin_Head]

That does’t explain why the other dash lights are on inappropriately.

 

[emac]

Dont disagree. I am no expert, but this seems to be the norm when the alternator goes bad in the 62. I have read lots of posts where this occurs. They are on the same circuit. I dont really understand it either. I will check all the grounds when I replace the dashpad. Seems like a ground issue doesnt it.

 

[FJACS]

If you follow the wiring diagram you will see that the lights coming on as you indicate suggests the system is working properly for a no charge situation. Follow the yellow/green ground wire from the charge lamp to approx A 14 on the wiring diagram. There is a connector here that sends a red/white wire to the brake light and a yellow/green to the transmission computer.

When the charge light relay grounds out (circuit completes) the red/white wire completes the circuit for the Brake warning light (ahead of the parking brake switch & low fluid switch) This illuminates the brake light.

The yellow/green to the transmission computer activates the a/t heat light.

 

[ToyotaDon]

The diode inside the relay says current can only flow one direction through the magnetic coil. Therefore, the relay can only be turned on when power is at the BLK-YEL and ground is on the YEL-BLU. For that to occur, the Charge Fuse has to have no power (essentially providing a ground) and the Engine Fuse has to be powered by the Ignition Switch. Once the engine starts, the Charge Fuse should have power, and the relay coil will no longer be energized, thus turning off the light. The point of this is that the Charge Fuse circuit is really what turns the relay on and off.

Now we are left wondering what role, and even what signal, the BLK-YEL Alternator to Charge Light Relay wire has. It would not make sense for it to ever provide a ground, as that would blow the Engine Fuse, so it must be a redundant power source for the relay.

Hope that helps with your mystery.