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Toyota Service
Toyota Service, Toyota Expert
Category: Toyota
Satisfied Customers: 4915
Experience:  30+ Yrs of auto experience, Award Winning Svc. Manager; Just Answer Customer's Choice Award Winner
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90 4runner, 3.0/auto. Not charging, new alt, good fuses,

Customer Question

90 4runner, 3.0/auto. Not charging, new alt, good fuses, good fusible link. What else?
Submitted: 1 year ago.
Category: Toyota
Expert:  Toyota Service replied 1 year ago.

Hello. Welcome to Just Answer. Please allow me to assist you. The following fuses are critical to the operation of the charging system:

7.5 amp Charge

7.5 amp Ignition

10 amp Engine

40 amp Fuse link AM1

Depending on your model, the 60,70,80 or 100 amp ALT fuse link

Ignition and Engine fuses are under the dash on the left side.

The Charge fuse, and fuse links AM1 and ALT are on the panel in the engine compartment

If all of these fuses are good, I suspect you have a faulty replacement alternator. This is not uncommon these days. We see alternators (and starters) that are inoperative right out of the box.

Customer: replied 1 year ago.
I replaced the alt with another reman. It tested good out of the box at the store. Once installed, it is saying the voltage reg is bad. Still not charging.All fuses are good, including the fusable link, checked on a meter.
Expert:  Toyota Service replied 1 year ago.

What is the voltage output of this alternator?

Customer: replied 1 year ago.
It is battery voltage, whatever that happens to be at the time of testing.
Expert:  Toyota Service replied 1 year ago.

If the alternator is properly producing the necessary current, it should be outputting 14.4 volts DC with the engine running and all of the accessories on. (headlights/rear defroster/heater or AC). If not, the internal voltage regulator is faulty inside the alternator. Measure your voltage at the wire lug on the alternator to the battery negative post.

Customer: replied 1 year ago.
Recap: alternator one did not produce, later tested bad.Alternator 2, tested good before install. Did not produce. Test showed bad internal voltage reg. Had enough of O'Reillys, went to NAPA. Their reman (now alternator 3) tested perfectly 5 times in a row before install, I witnessed it myself. Is still not producing. Post on alt shows battery voltage, NAPA tested it and told me it was working but not receiving the signal from wherever.Wits end here. I have opened the entire charging systemwire loom from the alternator across the radiator to the fuse box. I'm hoping to find something, anything wrong. I am preparing to replace the three wires just so that I know they are good.
Expert:  Toyota Service replied 1 year ago.

The issue here is most likely poor alternator quality. They can 'test' it all day long, and it might pass. Hook it up to an engine, where it is hot in the compartment, and several other things that are not found on the test bench, the alt may fail. You need to take this alternator back and go to another place to get a totally different alternator. There si nothing in the harness that will kill the charging; it is all internal in the alternator.

Customer: replied 1 year ago.
thank you for verifying that for me. I was pretty sure about that but it was being insisted otherwise. in the process of replacing the wiring which I am almost done with right now, I discovered hey Scott where the positive battery terminal breaks into two parts. And it just broke into two parts. The part that would have no longer have a connection has the 80 amp fuse and a fusible link on it. If that connector had been getting weaker and weaker, could this be part if not all of the problem?and in response to a comment you made, the alternator that is installed right now came from a different line of stores.
Expert:  Toyota Service replied 1 year ago.

A poor battery connection can trick the voltage regulator, yes.

Customer: replied 1 year ago.
the battery terminal issue was wishful thinking on my part. There is still no change in the vehicle.I was told by someone to measure voltage at the 3 wires of the alternator plug while the key is on. do you happen to know what the voltages should be?
Expert:  Toyota Service replied 1 year ago.

You should have 14.4 volts DC at the big wire lug on the back of the alternator (the lug with the nut on it), at idle.

Customer: replied 1 year ago.
Of course, am asking about the plug at the back. I am getting battery voltage, or close to it, on all but the red wire. Diagram says it goes to 10A Engine fuse under dash. Fuse still checks out good. Where does this wire go?
Expert:  Toyota Service replied 1 year ago.

The Red wire is the IG terminal wire. It is protected by engine fuse. The alternator plug wires are red, yellow/white, which are IG, L and the S circuits. You need to have power IN this red wire going to the alternator with the engine running. Please check for power in the wire and at both sides of the fuse whilst the fuse is in place.

Customer: replied 1 year ago.
I checked that fuse and there is power on both sides, but not at the plug. I will run a jumper this afternoon and see if it works.
Expert:  Toyota Service replied 1 year ago.