Battery light on and voltage issue
 

Just wanted to share a little troubleshooting adventure I had earlier today on my SC300. It's a 97 with 135K miles. Recently the battery light was on intermittently. It's the red battery icon down in the lower right hand corner of the dash. It was on constant, as oppose to flashing. This generally indicates that the system voltage (alternator output) was not high enough above a certain threshold I think it's 12.0VDC. It usually means when this light comes on that either your battery or alternator is on its way out and needing replacement soon.

What I was doing with that is that I ran the motor up so the RPM got to above 2-3K and the light went away for a few seconds and returned after the RPM got down to around 1K. As I kept driving with this, eventually the light would stay on constantly despite me revving it to 5-6K. My car is an OBD2 so I hooked a scanner and monitored the battery voltage during my trip. I noticed when the car was off, it would read about 12.6VDC but as soon as the car starts the voltage would dip to 11.5VDC and LOWERING constantly. At one point the voltage dropped to 8.9VDC and the car sputter ever so slightly and the ABS light come on. I started to turn on some accessories, my headunit, AC, headlights and lo and behold the voltage jumped back up to 13.6VDC after I had the headlights switched off. I have a eBay Xenon HID 50W kit and despite they are still operational, I suspect the ballast have developed a short that cause a huge drain on my charging/electrical system.

Tomorrow I will look at my headlights further but at least I know it's not my alternator. This whole time the battery light was on I was pretty sure I had to replace the alternator due to the pool of engine oil I found dripping on it from the distributor. I may have to replace it soon as some point due to the oil leak but not today!

You will need to replace your distributor o-ring (at the least, I had to replace my whole distributor because the whole thing was leaking), and your alternator is most likely toast.

Your voltage jumped once you turned on the accessories because your ECU cranked up the idle speed which increases power output from the alternator. From what I remember, at idle you should see between 13.8-14.1 volts.

alternator is going out, you can just replace the alternator electrical thing thats in the alternator.
it has the diode and resistors in it.
best to just replace it with a used one.
check fuses to.
you can take the alternator to auto zone they can test it to.