1996 LS400 dying while the car is running

[cooperd7]

I recently purchased a 1996 LS400 with 127k miles. While the car was on, it died on me and it would not turn back over. I have had this problem twice now, the first time, I was parked for about 5 minutes after a short drive when it had died, I was able to get it jumped and it ran well for 2 days. The second time, I had come to a stop at a red light and as i was about turn it died on me again. If anyone knows the problem or has any ideas on how to fix this please let me know. 

[Lexus Owners Club]

Hi...welcome to the Club

If it had to be jump started then it must be the battery has failed.

Whether it has failed because of a faulty alternator is another avenue to explore.

I would start by getting the charging circuit checked and go from there

[Bykfixer]

There was a time when the alternator/generator ran the car without needing a battery after the battery had been used to drive the electric starter motor that cranked over the engine and got it going. So in essence you could start your car and pull off a battery cable and the car still run. 

Largely you can still do that yet these days there is a symbiotic relationship between battery and alternator. So it may be as simple as crud on a battery post or a faulty ground wire interupts that relationship. In turn it may cause the voltage regulator, now inside of the alternator to prematurely give out. 

I used a pair of painted terminals on a car once. Painted between the battery post and terminal interupted proper circuit flow and murdered 3 alternators before I took it to my mechanic who said "painted terminals, dummy?" He also said dirty battery posts or terminals can do the same thing. 

I had a Chevy truck for work where the ground wire next to the battery had exposed wire. Weathering of the exposed wire caused issues with charging the battery so at times although truck ran 8 hours or more the battery would not receive a charge. 

In both cases no charging system malfunction lamp lit up. So it could be as simple as a ground wire is dirty where it connects to the engine block. 

[cooperd7]

I had my battery and alternator tested the day of the 2nd time dying, they both tested perfectly fine. Could it be the fuel pump or timing belt? 

[threepwood]

Just saw this.  Does it turn over but does not start?  If it does not turn over (crank) at all (just goes click, click) then it is not the fuel pump or timing belt.  My guess is still the battery but just a guess. How old is it?  3 years is about all you get here in florida :).  I know that my Mazda will not run without the battery connected but I have never tried it on the Lexus.  They are both 1990s vintage so it could be the same.  PS - I bought a cigarette lighter digital plug in voltmeter for mine (highly recommended) and eventually found my issue to be the switches in the vanity mirror of the sun visors were keeping them lite even when car was off.  I pulled both bulbs.