1990 LS400 was being driven on the highway for 3+ hours. No issues. Most of the warning lights on the dash start to light up and car starts behaving like the battery/alternator is dying....dimming lights, engine missing, and finally car dying. At this point all of the lights were out, and car would not even turn over. At this point I thought for sure it was a dead battery/alternator.

I went home and got my tools and returned 2-3 hours later. To my utter disbelief, ALL lights were on and working and car fired up normally like nothing had ever happened. I'm quite certain dead batteries don't recharge themselves, so it's clearly something else.

Is this the common trunk wiring loom short issue?

Any ideas are greatly appreciated. Car is needed for an out of town road trip very shortly, so I'm hoping I can get this nailed down ASAP.

 

first stop to any 1LS electrical issue: http://www.lexls.com/tutorials/lighting/bulbout.html

rule that out before looking into anything else.

 

Opened up the trunk wiring harness and inspected it. No cuts, no nothing. In as-new shape.

What's next on the list to check? Anyone have an DIY for checking alternator function with a voltmeter?

 

batteries do recover a bit with time, likely an alternator issue, and like caused by power steering fluid leak on to alternator - how old is the battery?

if the battery is more than 3-4 years old, I would replace it anyway, once a new battery is installed, take a multimeter and give us a voltage reading across the battery terminals, should be 13.5V or more at idle, and battery should be able to hold 12.6V with car off

be sure clean the battery terminals, and that includes unbolting the positive cable a couple of inches down where it connects to the terminal, they like to corrode in hidden areas of that connection