I just recently bought a 2003 LS430 with around 170k miles on it. At first it drove great. Until I got home and it wouldn’t start. I tried charging the battery and once it was at full I started it and a bunch of weird stuff started happening. The dash lights would flicker on and off as I tried turning the key, and the hazards would do the same. I did some research and thought it was a grounding problem. I couldn’t figure it out so I took it to a mechanic where they told me I should replace the battery and alternator. After replacing the battery I also noticed that 5 fuses had blown from a reverse polarity jump start. After replacing the fuses the car worked kind of normal. I had to rev the gas for the dash lights/other electrical components to turn on. All the electronic parts worked, but some components went a little crazy. The speedometer kept dropping to 0 and then back to 40mph, and the dash lights would dim and flicker. I then replaced the alternator about a day after all of that and then tried to start the car. To my surprise, none of the electrical components worked. I was able to start the engine, but it wouldn’t come out of park, the radio, dash lights, seats, etc would not work. The only thing that worked was the headlights and hazards. Now the battery has been drained by who knows what. I’m new to this, and I think it still might be a bad ground. Help!

 

You're right it probably is a bad ground. You will have to get really comfortable with the wiring diagrams to figure this one out. Are you able to use a OBD2 scanner to check codes/view live data? When did the backwards jump start happen?

 

The OBD2 scanner wont work, I don't know if the car has to have power for it to work or that it just not working. The backwards jump start happened about three days after I bought it, when the battery died the first time. While replacing the alternator I saw a braided copper wire with some corrosion on it that was bolted to the alternator. I cleaned it, but I still don't know if that was a ground wire. In fact I don't know where any of the ground wires are.

 

Yes the key has to be in the on position. Do your headlights work? Dome lights? Look at your battery negative cable and follow it to where it connects to the body is it damaged?

 

Yes, only my dome lights and headlights work. I'll check my negative battery cable today

 

If the headlights are operational your battery cable is likely fine. Like I said you'll need to get the wiring diagram to figure out what's going on. Do you have a multimeter or test light? Pull the cluster and check the ground and power supply on the connector.

 

Your "body ECU" may require attention..

Multiplexing saves wiring and weight, but when Body ECU fails, then it is not simply a matter or one system down, but many.

Experienced similar symptoms on my 1999 LS400, however mine was connector bulkhead getting wet due to plugged moonroof drains.

Unplugging drains and drying connector solved my issues.

Obtain a spare body ECU and see if that works.

Remember to disconnect negative battery cable. avoid "hot swap".

 

You should also check ALL your fuse boxes and relays if you reverse jumped the car. It sounds like you are getting partial power to only some stuff and that means you still likely have blown items and/or as Yoda said you fried a module from negative voltage.

Just go from battery to the first set of fuse boxes and then from there down the chain until you find where power stops. The item it stops at is the issue

 

Which "Body" ECU would you recommend the OP swap out? The 430 uses over 40 independent ECUs!
The sunroof has it's own ECU, the tilt and tele (steering wheel) motors operate from their own ECU.....................
It's a very long list.

 

Do you know where I could find the wiring diagram?

 

https://techinfo.toyota.com/techInfo....toyota.com%2F

Or

https://www.ebay.com/itm/2002-Lexus-...AAAOSwVqlaNC~C

 

The main 140amp alternator fuse was blown. Thank you guys for your help!!!