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Ted Ritter
Ted Ritter, Toyota Master Tech
Category: Toyota
Satisfied Customers: 4447
Experience:  Toyota Master Tech, ASE Certified
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98 4Runner: battery light..belt..tight..engine off, I have 12.6 volts

Customer Question

The battery light on my 98 4Runner came on. The alt. belt is tight, as are the cable connections. With the engine off, I have 12.6 volts across the battery. With the engine running, I have 14.5, even with lights, high beam a/c and full blower. Any ideas?
Submitted: 5 years ago.
Category: Toyota
Expert:  Ted Ritter replied 5 years ago.

ted ritter :

Hello, have you checked the 7.5A alternator fuse in the fuse box under the hood.

Customer: replied 5 years ago.
Hi - I was out of town the last 24 hours (different vehicle). I just checked the fuse and it is fine.
Expert:  Ted Ritter replied 5 years ago.
According to the voltage readings you are getting the alternator seems to be charging the battery. I'm going to have to look at a wiring diagram but it seems the battery light is grounding somewhere which will turn it on , this could be in the instrument cluster on the circuit board at the back.
Expert:  Ted Ritter replied 5 years ago.
Check the gauge fuse on the inside fuse panel, if the fuse is ok the alternator may be shorting the light circuit to ground but still charge the battery.
Customer: replied 5 years ago.
All the fuses in the driver's side dash are OK
Expert:  Ted Ritter replied 5 years ago.
Hello, other than giving another alternator a try I have no suggestions.
Customer: replied 5 years ago.

I have a 3000 watt inverter installed and I assume it makes a lot more work for the alternator. I have replaced 3 alternators over the lifespan of this truck. (560K miles).

But every time the alternator has failed in the past, I have always gotten less than 13.5 volts at the battery with the engine running. The alternator seems to be still working as I'm getting 14.5. Do you think alternator failure is likely in the near future? I don't mind swapping out the alternator, but I'd rather not if the current one is still OK.


Expert:  Ted Ritter replied 5 years ago.
Something is keeping the light on and yes I agree that a 3000 watt inverter is going to put a lot of extra strain on the alternator so yes it would seem likely that it's going to fail, I think that the circuit that is supposed to provide voltage to the light may be grounding internally which will turn the light on since it has 12 volts going to it from the other side.
Customer: replied 5 years ago.
OK, I'll swap it tomoorw and see if that solves the problem.
Expert:  Ted Ritter replied 5 years ago.
Sounds good, I'll talk to you then
Customer: replied 5 years ago.
Hi - I replaced the alternator. The battery light is still on.
Expert:  Ted Ritter replied 5 years ago.

Sorry to hear that, the light is getting a ground somewhere, i was hoping through the alternator. The light get 12 volts applied to it when the key is on and the other side is grounded to keep the light on, when the engine is running 12 volts is applied from the other direction, this causes equal voltage to both sides turning the light off.

On the black connector on the alternator are three wires, one of them should be grey, this goes to the light and also to the body ecu. With the engine running and the connector connected backprobe the grey wire and check for voltage there, if there is no voltage check to see if the wire is grounding with the engine still running.

Take your time I'll be offline for about an hour.

Customer: replied 5 years ago.
That was it. The gray wire is broken off at the connector. What is the best way to fix this? Can I get a new connector and just splice it into the existing wiring or do I have to replace the entire harness?
Expert:  Ted Ritter replied 5 years ago.
You should be able to remove the connector from the plastic housing and solder it back together. Look inside the connector there is usually a retaining tab that you can depress to get the metal connector out.
Ted Ritter and 3 other Toyota Specialists are ready to help you
Customer: replied 5 years ago.
Sounds good - thanks for your help
Expert:  Ted Ritter replied 5 years ago.
You're welcome, thanks for accepting.