When my alternator was going out I knew because whenever it wasnt charging every light on the dash lit up . I replaced the alternator . All the lights are still lit up but the charging system test at Autozone said that my charging system was working perfectly. What could be causing this ?

 

Hello,

What do you mean by all the Lights being lit up? A picture would be helpful.

Start by using a scan tool to see if there are any codes stored in the system, any major car parts store should be able to lend you a scan tool for free if you don't own one. If the car works fine and there are no fault codes in any of the systems, it may be a fault with the instrument cluster, though it is hard to tell without having a complete idea of what the problem is.

Hope this helps and best of luck!

 

When ya say all lights lit up, are you referring to all the lights in the dash cluster that come on when you turn the key before it starts and they stay on after the car is running? Sounds weird, I never had that happen. When my alternator was bad just the battery light came on. (also with a bad battery) It might be something with the cluster itself or something needs to be reset. Someone else will know more then me on this one but they would need to know the year of your car. Alot of things change over the years and different generations of the LS400.

 

The dash lights that stay lit are the Battery indicator. The thermostat indicator and the oil pressure Indicator. Now I just replaced the oil pressure or sending unit AND the thermostat. The battery is good according to Autozone and I havent seen any indication that it is weak , like the speedometer needle is usually the first thing sign.. Idk if thats how it goes with all first gen LS400's or just mine. She has been renamed the Lexorcist atm, hopefully thats temporary because I miss my Sexy Lexy. ILet me also say that I have very recently changed my alternator and power steering pump, plugs, wires, thermostat, oil pressure unit, and the weird little cover plate thats on the passenger side of the block because the seal was bad and leaking my coolant. I have not been able to burp the system with that top bolt by the thermostat housing because nothing i have tried. PB BLASTER. BREAKER BAR, PIPE WRENCH, has been able to loosen that bolt. I did, however fill the system where my thermostat goes and loosened the small hose to burp it while keeping the reservoir filled. and the car running. It seemed to improve but I havent tried another trip just yet.
Lastly. my brake& taillights are not working and I have to use shift lock release to get out of park. Last year I replaced the brake light indicator box in the trunk. I have not re-inspected it to see if its damaged AGAIN, I thought i should check the ? Brake switch?. I am a female and mechanic is not my field of expertise, but my car is my baby for the last 7 years and Im not above learning to do it myself. I have a lot more time than money lately and the price always goes up as soon as you say LEXUS!
My sincerest apologizes to throw this other stuff in there but I thought I should to get the big picture.. I love this car but maybe we arent compatible anymore and should break up!! LoL.
HOW DO I RESET MANUALLY IF I HAVE NO OBD-1

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It sounds like the brake switch on the pedal might be bad or the connections are not good cuz you can't shift from park. There might be more to that which someone else would know.
By "reset" do you mean the ECU? If so I just unhook the battery for a minute or so.
When I started to have battery/alternator problems the first thing I noticed was when I hit the brake pedal every light would dim.

 

What do you mean by the Thermostat light? The car doesn't come with any lights to notify about the engine temperature or the thermostat, it only has a Temperature Gauge. A picture of your cluster with all the lights on will be helpful.

The lights described are basic lights that are routed straight to the Instrument Cluster, without any ECUs in the way. Try disconnecting the oil pressure and alternator pigtails, not the round terminal held up by the bolt though, and see if the lights will turn off. If not, you either have a short in the wiring, or the instrument cluster is bad. If the lights will go off, then you need to look for problems in their respective systems.

Did you get the new alternator at AutoZone as well? Those are really not the best options, they are known to fail rather quickly. Here is a thread on diagnosing no charge condition, if the alternator is indeed bad, I would suggest getting a Denso Rebuilt option.

Are you sure it is the Pressure Sensor near the Oil Filter, and not the Level Sensor in the Oil Pan that you replaced? Those cars came with two different Oil Lights - Amber and Red. Amber light is for the Oil Level, it notifies the driver if the level drops below a certain level, but the sensors that measure said level, fail pretty regularly, and they are hard to come by, even used ones. If that is the light you have, it is safe to disregard for now, as long as the level is right.

Red light, however, is for the Oil Pressure, if it is on, and goes off when you disconnect the sensor, I would really suggest to ask a mechanic to check the engine oil pressure, those sensors are bulletproof, so the chance of it being failed instead of lack of oil pressure are slim.

Hope this helps and best of luck!