My 1993 ls400 was giving me all the normal signs of failing alternator. Headlights went dim when pressing the brakes, fan would cut out if the lights are on, etc. I installed an oem alternator from a reputable seller on eBay And everything was fine for a few days. I then went to start it one morning, and the engine started idle surging really bad, going from 500 to 2000 RPMs. I checked the battery voltage, and it was only reading 9.6 volts - however the alternator output was still sitting at 14.5 or so. I went out and bought a brand new battery from Costco. Again, everything was fine for a day, then the battery light came on as I was driving home. Just before getting home the idle started surging up and down again. After being turned off for about an hour, I went to turn it on and found that the battery was dead. It's not turning over, etc. I used the amperage setting on the voltmeter to test for a parasitic drain and couldn't find anything. I also don't believe it's a parasitic drain because I don't think the battery light would come on as I was driving home on the highway If it was a drain. to me, these issues are pointing towards the alternator again.... I also put on brand new terminals And made sure most of the connections were secure. I'm wondering if the original battery had a bad cell, which in turn messed up my new alternator.

 

Your power steering pump is not leaking and dripping ATF onto and into your alternator?

Check all negative grounds, cables and battery terminals.

Next check all postive terminals and cables.

Then all fuses and fusible links. (Stay with dealer on fusible links)

One simple check for excess resistance in the electrical system is to place your finger onto area where ignition key inserts into key slot/ignition switch.

I mention because my key switch area was really warm and surmised this was due to excessive resistance somewhere in the electrical system.

Sure enough, I had forgotten to fully tighten my negative battery lug...which increased resistance(and heat) across the circuit.

 

Of course this happened before I left town for a week, so I won't have the chance to go over everything until I'm back. I'll peek at the alternator to see if it's being leaked on but the old one didn't have any signs of this. I'll check my connections for the battery terminals, as well as the volt output of the alternator once I'm home.

 

The OEM is a Denso rebuild,thats what you got?

 

Oem denso that was tested and confirmed working.