Had a similar experience, and just to be clear, the only thing I know about the electrical system is what I read here.
I have 1998 GS300. Battery was drained while at work and when I jumped car at end of day, the alarm kicked off as soon as I attached jumper cables but the car started immediately after all jumper cables connected.
When I started to drive away, I noticed that all instruments were out on dash board. No MPH, No RPM, No Fuel or Oil. No backlight.
I checked Guage Fuse in kick box to left of brake pedal below steering wheel.
It was fine. Still no instruments.
Then I went under hood to fuse box on passenger side close to battery. I pulled a single fuse, labed MPX-B. It was fine and when I replaced it, the car alarm started.
Now when I went to start car, all the instruments and the backlight was working again.
Not sure if pulling the MPX-B fuse caused some sort of reset, but everything seems to be working fine now.
