Hello everyone! I am new, here! Please bear with me a little bit.
I am having intermittent electrical problem with a 1996 LS400. Some other day it worked fine. Today it quits on me. This problem has been going for several month. I would not dare to drive too far away from home. I am trying to find the root of the problem. When losing power to the car (that I could not start the engine) I found at this time no power to the following items: no horn, no clock, no radio, no interior light, no door light, no ignition switch light. Dash board gauge-speedometer still lit, power windows still work, seats still work. I already check all connections around battery terminals, cleaned them well, battery fully charged, fuses (under the hood & under dashboard) related to starter&ignitions checked. I love to troubleshoot problems but do not know how Lexus wired the car. Please share with me if you can. Thank you.

 

Welcome to Club Lexus.

Does the battery test ok? How is the alternator testing out?
Any dash warning lights/codes?

 

As I see the circuit diagram of a Japanese domestic model Celsior 1996 model, it looks like a loose connection of "the 80A main fuse line" shown below by a red line.


Sorry that it is for a Japanese model and not for an American model. I don't know it is the same or not, but there must be some similarlity regarding this area. Those red capital characters are the translation by me.

The horn, clock, radio and interior light are connected to the battery via small fuses and a 80A bigger fuse. I think this line has a problem on your car. Did you check the 80A fuse or the line connected to this?

Hope this helps you to find the point and fix the problem.
Yamae

 

I forgot to mention about the 20A EFI fuse located 5th from the top in the J/B No.2. The line is connected to the" メインリレー(EFI)" or "Main relay (EFI)" in English at the downstream. Your loosing power, VinhTran, must be caused by no 12V supply to EFI (Electric Fuel Injection). The 80A fuse line also supplies 12V to EFI, you know.

I also have to add some more translation. The left top box "FL ボックス” is "FL Box". The actual location "FL Box" is located next to the battery in the engine compartment. From "FL Box" to "2C" of "J/B No.2" is wired by a "白－赤" or a "White-Red" colored wire. Check the voltage of this "White-Red" line or the terminal "2C". I think the voltage there is much less than 12V or almost 0V. If this line is not active, your symptom, losing power, no horn, no radio and no interior light problems will occur judging from the circuit diagram.

Best wishes.
Yamae

 

Here I add the location of FL Box and J/B No.2. Those are indicated by red characters
But please remember that this drawing is for a Celsior. I think the LS400 is almost the same.


Yamae