I suspect I have a dead alternator, but before getting a replacement ($$$) thought I would ask about anything else it could be. Last week I started my car up and several unrelated instrument lights stayed on. The car ran fine though, but after a couple of miles I realized the daytime running lights were not on, so had to turn lights on manually. Next day, same story, but then ABS light came on too, then whole instrument panel started flashing, then the car died. Would not crank at all when I tried to start it. Fortunately I had an emergency battery pack, so hooked it up and car started. Only lasted a few minutes though, then it died again. Did this a few more times before I got home.
I recharged the battery, which was drained, and then the car started fine, but the instrument lights were still on. I figured it was probably the alternator. Tried testing this by disconnecting the battery, and car died instantly. (Note: this is actually not a good thing to do, as if the alternator is good it can fry the instrument cluster.)
So, fellow weekend mechanics, is it the alternator for sure, or could it be something else? Had a look at fuses, which all seem to be ok. Not sure about regulator. There does not appear to be any leaking from power steering onto the alternator, but I did change coolant a couple of weeks ago, and that might have gotten onto the alternator.

 

Sounds like the alt. to me b/c it runs with a fully charged battery until ya disconect it. They don't last forever. What year, how many miles ya got? I got my alt from the J/Y for, I think, $35. Alot better then spending over $200 for a reman. Even if I change it 3 or 4 times I still make out financially. If you're doing this job yourself you might as well plug that valve on the power steering pump while you're in there and have the room.

 

Take car to Autozone. They will check your alternator for free. Also,I have a '92 LS400 and I took my alternator off and took it to a local alternator repair shop. They charged me $ 40.00 to replace the brushes. I watched him do the job and its very easy. The brushes just shap out after you remove the back pieces. They are white and shaped like
a ring with a big diamond head. Should be able to buy brushes from auto parts store or
local alternator repair store. It was also a good time to clean up my alternator and remove all the grime and dirt.

 

Alt is usually indicated by the check engine, brake and lights. Get it fixed soon...a deep discharge on the battery is hard on them and this may lead to a shortened lifespan.

 

Plug what valve on the PS pump? It is a 1991 with 160,000 miles on it. I pulled the alternator ... man what a PITA to get out of there. I will look at the brushes, but I found a used alternator for $80.

 

Using a used alternator is OK, but I would at least check the brushes and have it checked at autozone or other parts store to make sure its OK. Even so, its good insurance and cheap to change the brushes. There are a number of detailed posts
on removing the black cover on the bottom of your pump and removing the insert
fitting that goes into the pump. You will need to remove the two small hoses ends that connect to the black cover up on top of the motor and plug the holes. You will need
a plug for the bottom of the pump also. I could not find any suitable bolt/plug in my
bolt bucket and had to go get a plug at Autozone. They cost $ 4.99 or $ 5.99 and also have a rubber ring built in to help prevent leaks. Take the old insert that you remove from the bottom of the pump-this will help you get the right plug. I think the one I got was a oil pan plug- but I'm not sure. I would get it at autozone and save yourself a trip to the hardware/ rurual supply store and end up spending a lot of time
trying to match up what you need and not have any results. BTW: Its no big deal to remove the back chrome heat shield on the alternator and the othe parts/bolts screws; no complicated to re-install part is going to fall out as you remove the items to get to the brushes. (Added note: There a several good posts on this site and a related tutorial site that caters to LS 400s that go into detail and provide pics to help you on the pump. )

 

Check the ignition fuse in the fusebox in the footwell. I hear this can cause dead alternator symptoms

 

I changed the alternator, and the problem has gone away. Posting this so that anyone else having similar problems knows what to look for.