Bizarre Electrical Issue

[viker123]

Hi,

New to Forum but it seems you have the answers !

I have a 1990 LS400, one of first delivered from Longo Lexus in El Monte, CA. Absolutely zero problems until recently.

I was driving on a somewhat long trip( 6 hours) and about 1/2 way, all the dash lights came on. The engine seemed OK, but I stopped and called my son.

He arrived and the car started right up, no dash lights other then normal at start up then go out.

Now getting dark so had to turn lights on. I was almost to my destination, when headlights got very dim and engine started to sputter. Turned off lights, engine caught and I made it into my driveway and it quit completely.

Next AM, it started and I checked and ZERO output from alternator.

Charged battery, ordered new alternator and when it arrived, I went to install, but gave alternator a check again and guess what? IT WAS PERFECT ! Drove 70 miles with lights on and all electrical and rechecked and zero problems. Over 14 amp output ! No PS oil on old alternator.

Any ideas? Is there a relay of some sort? Kinda nervous about going on road again.

Thanksfor your help

[landar]

Welcome Viker. Have you had the notorious, bizarre trunk wiring cable checked out? Although I doubt that would cause the headlights to dim. Possibly the main 120 A fuse or connection is intermittent. The most obvious place to start is with the battery and the cable post connections. Make sure the connections are clean and tight and that the battery is good.

[viker123]

Welcome Viker. Have you had the notorious, bizarre trunk wiring cable checked out? Although I doubt that would cause the headlights to dim. Possibly the main 120 A fuse or connection is intermittent. The most obvious place to start is with the battery and the cable post connections. Make sure the connections are clean and tight and that the battery is good.

Hi Landar,

The lights dimmed as the battery had finally run out of juice. As I stated, the engine picked up as soon as I turned off the lights and I made it the final 1/4 mile to my home.

Where are these mysterious 120 amp fuses located? Does the owners manual show a schematic?

thanks for the response.

What I really don't understand is how it now shows a full output from the alternator although the bad connection may be the source.

Terminals are clean and tight on battery.

Thanks again

[landar]

Intermittent problems act just the way you have described the symptoms. Your old alternator could still be bad at times. Perhaps an internal diode is opening up (open circuit) when it gets hot. In any case, I would check your charging system very carefully to determine the root cause. There are literally dozens of videos and tutorials online describing how to use a simple VOM to check the charging system. If you do a thorough search on this site, you will see many threads devoted to issues such as you are seeing. Then sit back and enjoy the reading.

If you do not feel confident in checking your charging system yourself, you can take your car to most auto centers and they will perform a charging system check and load testing of your battery for a small cost or possibly free.

[1990LS400]

I would still first unwrap and check the wires at the left trunk hinge. The problem seems to affect 100% of gen 1 LS400s and sometimes must be fixed over and over as the wires "re-break" at another point. I had this problem on the 90 LS I drove from new to 2003 and its 2nd owner told me he had to fix the broken wires at the trunk hinge again some time after he bought the car from me.

[viker123]

Hello again all you experts,

I did all the tests recommended and rechecked the trunk wires. No breakes found in trunk, but zero output from alternator. Bit the bullet and purchased a new alternator and installed this date. Initial test showed max output when I started the car. I let it warm up as I cleaned my hands and then I turned on the lights and the heater and fan. Output dropped to almost nothing. I turned everything off and rechecked (engine still running) and it showed a better output then when loaded, but nothing like when I first tested it.

The alternator has a built in regulator I believe so that should not be the issue. It was mentioned a possible dirty contact somewhere? Terminal;s are spotless so tell me where I should be looking next.

Can't drive the car as have no trust ion electric.

Thank you

Vic

[lenore]

Did you buy alternator from Oreilleys, if so I had terrible luck with that retailer, put 4 alternators in my sons truck, they all failed prematurely....Bought one from Napa and was good to go.

[jaswood]

Hi,

New to Forum but it seems you have the answers !

I have a 1990 LS400, one of first delivered from Longo Lexus in El Monte, CA. Absolutely zero problems until recently.

I was driving on a somewhat long trip( 6 hours) and about 1/2 way, all the dash lights came on. The engine seemed OK, but I stopped and called my son.

He arrived and the car started right up, no dash lights other then normal at start up then go out.

Now getting dark so had to turn lights on. I was almost to my destination, when headlights got very dim and engine started to sputter. Turned off lights, engine caught and I made it into my driveway and it quit completely.

Next AM, it started and I checked and ZERO output from alternator.

Charged battery, ordered new alternator and when it arrived, I went to install, but gave alternator a check again and guess what? IT WAS PERFECT ! Drove 70 miles with lights on and all electrical and rechecked and zero problems. Over 14 amp output ! No PS oil on old alternator.

Any ideas? Is there a relay of some sort? Kinda nervous about going on road again.

Thanksfor your help

Marginal alternator slip rings or slip ring brushes.

1990.....

lots of miles...??

[viker123]

Hello Again,

This is giving me fits.

14.2 output from new alternator. As soon as I turn on lights, .46 output ! It is clear that when a load is placed on the system, it stops working.

Any ideas would be most helpful. This is a brand new alternator so don't think it is an issue with the unit itself.

Is there a relay or something in the system I should be checking?

Thanks

Vic

[viker123]

Hello Again,

This is giving me fits.

14.2 output from new alternator. As soon as I turn on lights, .46 output ! It is clear that when a load is placed on the system, it stops working.

Any ideas would be most helpful. This is a brand new alternator so don't think it is an issue with the unit itself.

Is there a relay or something in the system I should be checking?

Thanks

Vic

milage is only 112000

[curiousB]

Well maybe the heavy wire from the stud on the side of the alternator to the battery is corroded and limiting the current. The scenario is when alternator is lightly loaded no problem. Start turning on various loads and the alternator can't overcome the IR losses and you get the low reading. Where are you measuring this voltage and what point are you connecting negative? Could also be a poor ground from battery to chassis.

[viker123]

Thanks. I will chk tomorrow but my recollection when I replaced the alt. was the lead was clean w/ no corrsion.

I am measuring at battery terminals so that I can see if input to battery is a plus or a minus.

Thx

I will also chk ground from bat to chassis

[jaswood]

Hello Again,

This is giving me fits.

14.2 output from new alternator. As soon as I turn on lights, .46 output ! It is clear that when a load is placed on the system, it stops working.

Any ideas would be most helpful. This is a brand new alternator so don't think it is an issue with the unit itself.

Is there a relay or something in the system I should be checking?

Thanks

Vic

milage is only 112000

Let me get this straight...

14.2 volts across the battery terminal/posts presumptively with the engine running.

That would be NORMAL.

0.46 voltage across the battery when you turn on the lights...?? Engine still running..?

Not even remotely possible.

Light switch on = engine stalled....??

Then DEAD battery or poor electrical connections.

14.2 volts would, generally, indicate a HIGH battery charging rate.....a low battery charge.

[landar]

Thanks. I will chk tomorrow but my recollection when I replaced the alt. was the lead was clean w/ no corrsion. I am measuring at battery terminals so that I can see if input to battery is a plus or a minus. Thx I will also chk ground from bat to chassis

It does sound like IR loss. Check the wires that come into the battery post clamps. Sometimes a high z connection develops there where the wires meet the clamp heads. With several heavy electrical loads on (headlights, seats, defroster) you might feel some excessive heat at one of the battery terminals with your hand. They should be stone cold.

[lenore]

look very close at your battery cables, corrosion can go down the ends of the cable into the wire itself, under the insulation...I would put a ohmmeter on the cables on both ends to make sure they are good, and wiggle them to see if the resistance goes high...(should read approximately zero ohms) The only other thing is a bad ground...maybe corrosion where it attaches to engine block...

[VBdenny]

Could be any number of many high tech issues however, you never mentioned how old your battery is? I'll just say that these early LS400's need a LOT of battery. Cheapest place to start. Yeah, I've had places test them and say they were good but they weren't. You can get one cram packed full of juice for under $100, even less at Costco or place like that.

If your battery is more than 3 years old especially if you live in a hot region, I'd pop a new battery in and see what happens. It is also a very, very good idea to check the wires in the left trunk hinge. I've repaired 2 of them in the past. Really weird things happen when these wires break.

[viker123]

Thanks guys,

Battery is less then 1 year old and fully charged. I did same test today and got full output with load as no load !! Go figure. Drove it 40 miles and retested and got 14.2 with load and same w/o load.. I did wiggle positive cables as there seems to be two attached to that terminal. I will remove toomorrow and check for corrosion and clean.

I'll let you know what I find and thanks for the responses.

Vic

[viker123]

Well people,

all I did was take the cables off and take a look. They looked clean and zero corosion. Been a few days now and have driven both with and w/o lights and so far full out put back to battery from new alternator.. Have no idea what caused the prior readings. Speedo and tach seem a bit off and the cruise stopped working so I'll have to look see what that's all about !

Always something with older cars I guess !!

[VBdenny]

I still blame the battery. One year old doesn't carry any weight with me, nor does the auto stores "test" of them. Just a few months ago replace a 8 month old Advance battery which was failing. The auto parts store "test" showed it was good but when I showed them the diagnostic tests from the Toyota dealership, they put a new battery in right quick and N/C. I know this car needs a LOT of juice to run properly. If you argue with the place you bought it, they will replace it. Depending on how much they argue determines future business I guess. Otherwise check grounds. The engine to frame ground causes major issues when open. Same with the battery to engine ground. Of course if you have not checked the truck wires yet ....

[jaswood]

Well people,

all I did was take the cables off and take a look. They looked clean and zero corosion. Been a few days now and have driven both with and w/o lights and so far full out put back to battery from new alternator.. Have no idea what caused the prior readings. Speedo and tach seem a bit off and the cruise stopped working so I'll have to look see what that's all about !

Always something with older cars I guess !!

Rear brake light bulb failure, even just one, will disable CC.

Don't forget the high mount.

[viker123]

Thanks, I'll chk it out tomorrow.

V

[viker123]

Hey There,

All brake light bulbs operative. CC still inop. Blinks a couple times after engagement, then nothing.

Electrics still good.

Thanks

Vic