I was driving down the street and my car started to slow down then my VSC check light came on then it died. I had got a jump but it didn’t last long. I bought a new battery and got my alternator tested multiple times, it tested good. did the ‘remove positive wire test and the car dies. The battery light doesn’t come on at all. I changed out the IGN and ECU fuse and the alternator won’t keep the car charged

What is the battery voltage when the engine is running?

I don’t know I don’t have a voltage meter but it’s a brand new battery

Who has tested the alternator? One person multiple times, or different people? To me it sounds like a bad alternator or a bad connection somewhere. It could be the main power wire to the alt. or a bad (or loose) ground wire.

multiple people tested it autozone oriellys etc.. I had to put a new pigtail on it because the old one broke when removing the alternator. I’m fairly new to cars where would the ground be for the alternator

Get yourself a multimeter. No need to go to a shop to see if your alternator is charging or not. Takes all of one second touching the probes to the battery terminals with the car running. Should be seeing somewhere around 14 volts. Battery should be 12 volts (obviously), car not running.

You can also do a "wiggle test" with the probes connected to chase down a bad connection. Could be something as simple as a bad ground. Been there, done that. Clean everything.

I would be re-visiting that pigtail you replaced. How was it spliced in?

Invest in some basic tools if you're gonna run an old car like this or expect to go broke in a hurry.

This problem could be caused by a failing starter drawing excess current - quite common on the gen 2 LS400 as it ages. Here is a link to a thread about it: https://www.clublexus.com/forums/ls-...-ls-400-a.html

In my early wrenching days, I had a Land cruiser with a bad replacement alternator, which the auto parts store refused to replace because their machine said it was good, even though it was putting out something ridiculous like, 17 volts, which was tripping circuit breakers in the car.

Just my two cents.