Gs300 battery light won't go off
 

Whats up guys have a 1999 gs300 that has a battery light on but alternator and battery is good. I tryed 2 alternators and the light is still on. Battery is good and always starts right up no issues even if I leave it for a week. I checked the fuses including the 5a fuse in the engine bay. All terminals have been cleaned as well. cars runs well and all electronics work. Brake fluid is also full

Any updates? Genuinely curious as to what it could be. I'm wondering if your ECU batt is failing, it's a stretch, but might be something to look into.

Had the same problem. Mine would blink on and off, then one day it stayed on. New battery, new alternator so i know its something else. I changed out the harness because the clip was broken and that fixed my proboem. No battery light ever returned. Check all your wiring connections and fuse related to alternator and battery.

You should check the voltage making it to the battery with a volt meter and see if it's getting alternator volts. Check for corrosion at the battery terminals. If there is build up inside the terminals the connection between them and the battery might be impeded. Also look for corroded cables. If you can wiggle the terminals or cables and the light goes out, you know there is a connection issue.

Check the ALT fuse in the fuse box next to the battery. I saw it another thread for the same issue. If you have the electical wiring diagram you can see it there. let me know if you don't and I can send you a picture but it's self evident once you open the long fuse box in front of the battery (GS430 2003)

Edit: I just saw that you had already checked the ALT fuse and it was good. The only other thing I can think of is that the 3 wire back connector is the problem. I had to replace my alt connector after 17 years as it broke removing it. These are the 3 wires feeding the ECU etc so it could be the cultprit.

You can also check the cables with a multimeter. (GS430 2003 reference) Disconnect the battery (both positive and negative) and connect the meter to the ground (black wire) and the lower bolt on the alternator. the lower bolt connects the cable to the alternator and to the engine/frame. Resistance (Ohms) should read 0.5 or so ... Don't worry if its not exact as there are many issues that can result in higher readings such as dirt, oil etc. But if it's reading substantially higher, >1-2 ohms you need to clean the connection points and retake the measurement.
For the Red (+) terminal, you need to get access to the top nut / stud on the alternator and you may need to remove the air intake, 4 bolts or so that are easily accessible. and located the stud on the top of the alternator, remove the rubber cap and you'll see a bolt/stud connector and connect one end of the multimeter there (aligator clips work best) and then connect the other multimeter probe to the red positive battery terminal that is disconnected from the battery. Again you should read < 1 ohm.

The connections to the Alternator are all part of an engine wire loom and if you need to replace the cables it's best to research it more as it's more complicated fix. In my experience, the cables are not an issue unless there has been some damage done to the engine bay. There are fuses to prevent most electrical issues and damage.

Hope this helps!