Lexus LS400 Electrical Issues

If it is a connection issue, where could I start checking? The battery cables, cables running to the fuse box? The alternator is very hard to get to, but should I check the connections there as well? Just any advice on where to get started would be greatly helpful!

I will be sure to clean all the connections, and make sure everything visually looks fine. As far as the car cranking, it will in fact start. The problem is that once it is started, none of the electronics will work (headlights, cabin lights, gauge lights, power seats, power windows, radio, etc). I'm wondering if a dead cell (or any other internal issue with the battery) could cause electrical issues like this, or if the problem lies somewhere else? I plan on replacing the battery tomorrow, but I'm wondering if this will remedy all of the other electrical problems as well?

Basically I'm wondering if the battery is giving the car just enough juice to start, but since it is testing "bad", that it's not providing enough power, or the right kind of power, to allow other electronic functions to work?

Like I said, I can get the car to start, and run for short periods of time, but none of the gauges, lights, or anything other than the engine running will work. I know these Lexus's are very "advanced" and "technology savvy", so I'm wondering how dependent the systems are on a "good" battery.

Okay, thank you for your replies -- I really appreciate it. I hope that it is something simple like the fuses, but I sincerely hope it is not the alternator. Hopefully I can figure out what is causing things not to work. If it helps with troubleshooting (I'm not sure how familiar you are with Lexus's), in order to just shift the car into gear to move it, I had to press the "Shift Lock Override" button. Does this also sound like a fuse issue? Or what would cause something like that to happen?

If it is just a fuse, that would be AMAZING news! Thank you for all the advice! I will try to post back what the solution to these problems turns out to be, or if I run into any other issues!

Thanks again, Wrenchtech :)

Thank you again for the responses! Yesterday I checked all of the fuses in the cabin, and they were all perfect. I opened the hood to check the fuses/fusible links there, and sure enough, a fusible link, and 3 fuses were blown. In this car, there is a fusible link that is specifically for the alternator; it was completely blown and melted on top, so we picked up a new fusible link and a fuse tester while I was replacing the "bad" battery. The fusible link was a pain to get out, but once we got it out and replaced it, BOOM! All the gauge lights, dash lights, headlights, power seats, windows, etc started working, but there were still a few things that weren't. Apparently when this fusible link blew, it caused those 3 others to blow as well; the radio fuse, the "dome" fuse (I'm assuming this meant the dome lights? Considering they still weren't working after replacing the fusible link), and most importantly (ha ha) the telephone fuse was blown. Once these 3 were replaced, everything works perfectly!

Thank you so much for the quick responses; I was so lucky for it to just be a $26 repair (including new power steering fluid)!

I have not checked all the voltages yet for the alternator, but I left it running for about 25 minutes just sitting there with the radio on and everything to test it, as well as a few test drives, and it still had plenty of power (no battery light popping up on the dash, lights dimming, hard re-starts, etc)! I will check the voltages today in the daylight, just to make sure!