Mysterious stall/electrical power loss

[vltjr]

Sunday night my daughter's '90 LS400 stalled out, preceded by usual loss of (electrical) power symptoms (headlights and dash lights dimming, gauges zeroing out). When she tried to restart it, it seemed that she had a dead battery. I went out Monday morning prepared to change out the battery and get it moved to the house, and much to my surprise it started right up. I should mention here that the reason I was prepared to switch batteries is that about a month ago I replaced the alternator with a Denso rebuild, and my suspicion was that I perhaps got a lemon. When I got the car home I checked the battery, and the alternator output, and everything was okay. My daughter is understandably afraid to drive the car until I diagnose and correct whatever caused this malfunction, but I'm at a loss as to how to proceed. I've been driving the car on and off since picking it up hoping that the problem would recur, but it has been starting and driving perfectly.

Anyone have any ideas? Thanks

 

[cribbj]

I'd be looking for a dodgy connection between the battery, alternator, engine, and chassis.

Check the negative (earth) connections, as well as the positives. A bad earth will shut the car down as fast as a bad positive connection.

Since you just replaced the alternator, it's possible that the connections weren't tightened back up completely.

Be sure to check all the high current cables and connections, however.

 

[vltjr]

Thanks cribbj, I checked the cables and various grounds (and cleaned them up), but I haven't found anything that seemed to be glaringly wrong. I'm not sure what "high current cable and connections" you were referring to, and I would appreciate it if you could clarify for me.

 

[Zuffen]

High current cables are such things as starter and earth cables from the battery.

Also check the large (fat) cables running into the fuse box/ECU.

For that matter check nany fuses/fuse holders that run the ecu/fuel pump to make sure they aren't correded or dirty.