Hi all,
my trusted 1992 daily driver is giving me some issues.
It started when arriving home one day and parking, I started getting all sorts of lights in the dash (coolant, battery, oil, rear lights), dependent on the RPM of the engine. Idle to ~1400rpm nothing special, but anything above and the dash would light up.
Decided to limp it short distance to my garage the next day, but battery was too flat to start the engine. Charged the battery up with a trickle charger, limped the car to the garage keeping it under 1400rpm. Same behaviour as the day before - exceed 1400rpm and the dash would light up.

Without a second thought, ordered a reconed alternator and started swapping it. Firstly, noticed that someone has used the 1993 onwards type of alternator with oval connector, and used some jump cables to wire it up.

Needless to say that the original Round connector was quite messy, being out in the open with only jump-wires hanging out from it for the last 15+ years.
Gave it a good bath with cleaner, measured the resistance of the cables (B-cable 0,0 ohm, L-pin 0,0something ohm when ignition turned, S-pin 0 ohm all the time, IG-pin no connection, from my understanding not supposed to be if engine not running?)
Then swapped in the new alternator with the round connector.

Everything back together, battery charged with a trickle charger, started the car and... No charge. 12.1V on the battery, all the aformentioned lights on the dash again, idle at 2000rpm and won't come down, headlights not turning on automatically as they should.

I've checked all the basic stuff, like serpentine belt is on, pulley/generator is spinning etc. A horrible tought entered my head, that maybe this wasn't an alternator issue in the first place... Maybe there is a module gone horribly wrong somewhere..?
I'm gonna order a new round plug first of all, since that old one still looks quite horrid after the cleanup, and being wired up as it was there might be some twisted pins etc.

But what else should I check now? Get the old alternator tested somewhere? Make sure the alternator core itself has good ground with an extra ground cable..? Any ideas or similar experiences are welcome.
I do have some modules / computers left over from a parts-car that I used to have, so can try throwing some of them into the mix, if that's needed.

Anyway, hope you're good, greetings from the frozen north from my LS and aurora borealis

 

Hello,

Not sure how you checked resistance on power wires.. I would really suggest getting a simple Test Light to check stuff like that, it will never fool you like some regular household multimeters.

B+ Terminal is what supplies the charge to the battery, the only way to test it properly is to get several headlight bulbs wired in Parallel, or something quite powerful to make sure there are no breaks in the connection, like it was the case here.

Pin S is the Constant 12V supply, it should always be present.

Pin L is for the Battery Light on the dash in case the alternator fails to produce voltage. To test it, connect a Test Light to it, both the test light and the light on the dashboard should light up half-dim, since they are wired in Series.

Pin IG is the one I am particularly interested in, as it is supposed to have 12V supply when the Ignition is in the ON position, no matter if the engine is running or not. Here is a Fuse Diagram for your car, I don't have a service manual for a 1st-gen LS400, but in other models they used GAUGE fuse to to power Pin IG for the alternator. In any case, it won't hurt to check them all, and by using a Test Light on the exposed leads on each fuse, that task becomes a breeze without having to take each one out.

Also, couldn't help noticing that it is not an OEM alternator that you are using.. From my experience, it is pretty hard to find a solid replacement from the aftermarket parts, unless if it is a Denso Rebuild, which is unfortunately out of production by this point. With that in mind, it may be beneficial to make a better quality adapter for a newer style pigtail and use a newer alternator, it will greatly simplify your life as the time goes on, as well as avoiding any pitfalls with aftermarket alternators.

Not sure if you replaced the connector already, but there is a way to do it without cutting any wires, here is a link to that thread. If you can find a corresponding pigtail to that round connector, you can make a pretty descent adapter, that's how I installed some alarm systems.

Hope this helps and best of luck!

 

Finally got a fresh new round connector in the mail, wired that one and plugged it in. Still the same thing. Absolutely no charge (12.1-12.2V while running), idles at 2000rpm, all sorts of lights on the dash, headlights not automatically on.
Thanks for the reply! Interesting... If I remember correctly, I'm pretty sure I couldn't get 12v on the IG-pin with ignition on.
I need to remeasure some things for sure, now that I'm absolutely sure that the connector is spot on and definitely pushed all the way to its place etc. It is entirely possible, that the same previous owner who had McGyvered the wrong type of alternator in there, has done something funky with those wires too.

It is a remanufactured alternator from RockAuto, yes. "Pure Energy" brand, so not the cheapest, not the most expensive one.
Has anyone had bad luck with remaned non-oem alternators just outright not working..?

 

Anything but a Denso reman has a very high failure rate.

 

I would start by checking fuses, since this is the most likely place where it could go wrong, otherwise the wire goes straight to the Ignition Switch, so it's either the switch or the wiring somewhere in between.

Well, I'd say this thread about sums it up..

Hope this helps and best of luck!

 

Fuses I have checked. 120amp Alt-fuse, 40amp one (AM1 or something..?), and the ignition under the dash. They're all fine.
Wow, even not giving ANYTHING straight out from a box..?

I'll continue investigating when I have more time, but might just get lazy too and order a Denso remanufactured one in advance...

 

No. It seems crazy but true.

 

It's a 10A fuse somewhere on the Driver's side in the interior. Not sure exactly, but I think it's a GAUGE fuse to pay attention to.

 

Just go to your local starter / alt. rebuilder. Every town has one (or more). NEVER had a problem. Not one time. They won't be in business if they don't know what they are doing. And you can go straight to the guy that did the work if you do end up having a problem.

 

Little update here: Got money back from the alternator mentioned previously, bought a Desno remanufactured one insted, and lo and behold - it worked.
Thanks to everyone for the advice there.

My cold idle now seems to be stuck unreasonably high, like 2000rpm. Wonder if the faulty alternator broke something, or whether the module needs to "relearn" something, I've driven the car maybe 2 miles since I've changed the alternator, and it stood still without a battery for months.
Will drive some more once I get the chance, and report back.

 

I totally agree with 94V8coupe about using a local rebuilder for starter and alternator issues. I have one in town and the guy is a genius - and inexpensive too. You should see his shop, he has every piece of equipment imaginable for the trade including a lot of analog equipment dating to the 1970s and earlier and does everything from marine, to industrial, automotive etc. and gets it done right the first time. Doesn't even bat an eye if you bring in some rare, unusual, foreign, antique or other electrical motor or alternator that you cannot just go out and buy and HAVE to rebuiild. He could probably rebuild a Lexus alternator in his sleep...

 

I know nothing about what it actually takes to rebuild an alternator. But let me tell a story.

When I first bought this car, I had it serviced at a small independent shop with like 5 workers, well reviewed, and I could speak directly with the mechanics as you were describing the problems & working with them. They mostly worked on depreciated luxury; german and asian cars. These weren't guys who worked on F150's and Camaros. They felt like they cared. I didn't know anything, they diagnosed (what, in hindsight, were blindingly obvious) broken motor mounts as a cooling fan clutch. The fan clutch wasn't broken. They then put an aftermarket clutch which was frozen fully engaged, didn't fix the vibration I wanted fixed, and then proceeded to gaslight me that they're supposed to be like that. Took 3 visits before I finally forced them to put an OEM unit on the car, which remains on there to this day functioning perfectly.

I've been to 6 local shops at various points over the years. In my area, the best people to do work? It wasn't the actual Lexus specialist shop. They were very nice, but long story short, they have very high labor rates, and I ran some tests on them and they failed pretty spectacularly. The best people ended up being the strange shop tucked in a corner which for some strange reason always has a ****load of very expensive air cooled porsches parked outside of it that they do a lot of work on. Point of my story is, it all comes down to the individual. It can be really difficult to find a mechanic to work on your car, and the parallel I'm drawing here, it may be just as similarly difficult to find other specialists as well.

 

Driven ~600 miles now, and car has "relearned" it's idle. Back to normal(?) 1100rpm when cold, gradually down to 650-700ish when warmed up.

 

Sounds about right