peterls

EDIT: for the explanation on how to fix this issue and bypass the warning light module, go to the last post I made in this thread - the one I posted on Apr. 12, 2016!

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Hey guys, I could really use some help here.
Today I picked up my 1990 LS400 from a mechanic who replaced my starter and knock sensors. Everything was fine.
However, just now I noticed my brake lights are not working. For all I know they may have been broken since who knows when as I have not checked them recently. I do remember a few days ago that the shifter did not want to unlock when I pressed the brake pedal but then it worked fine after only misbehaving once or twice that day and never again.Right now, the break switch does work as it disengages the shift lock (and I can hear it "click" when I step on the brake pedal); I also have a good brake switch (oem) that I replaced today after I found out that brake lights didn't work, and brake lights don't work with the new one either (the shifter clicks and unlocks fine though).

I checked the fuse, and it looks fine - besides, if the fuse was bad , the shifter would stay locked as far as I know.
Then I climbed inside the trunk and with a strong flashlight inspected the wire loom in the trunk. Found one black wire cut clean as if by a knife (how the heck did that happen?!) - reconnected that one, and now my remote trunk release works. Yey, shallow victory...

So, it seems that somewhere between the switch and the brake lights there is a problem. Where could it be if it is not in the wire loom? How do I find it? which way do those brake lights wires go anyway - could the mechanic have broken them accidentally while he was working on the starter and knock sensor? (he did have a bit of a problem starting the car again after everything was done, because right ignition connector got disconnected, so I don't know where he might have looked and poked...)

I also see a little brake light warning indicator in the trunk - could that affect the stop lights?
BTW, other lights in the back work fine, when I turn them on. It is only the brake lights that don't work.
If you have any idea, I am dying to hear it. Especially ,as to where do the brake light wires go - do they go to the engine compartment at all, or do they go straight from the brake pedal, under the carpet and back to the trunk.

Thanks!

ps. Brake light bulbs are brand new, at least three of them were changed today.

Yamae

Yes.
Check the connector inside of it and the current sensing resistors. I have seen soldering points of those were cracked among very old Celsiors. Sometimes the connector was burnt partially.

peterls

Thank you Yamae. I just popped it open (the warning indicator ecu in the trunk) and the thing looks perfect inside and out. I took it out of the trunk so that I could inspect it properly - visually it looks fine. Caps are not crowned, no burned trace lines, nothing.

However, I did have stop lights go out a few times in the past and never had any kind of warning light come ON on the dash, so I thought that my car did not have the warning for the stop lights at all!
Now I know I have it, but it does not work.

Could you give me some pointers how to test the warning module? at least to make sure it is not cutting power to the stop lights? And maybe which connectors should have power, so that I can determine if the problem is before the warning module or after?

peterls

Just had an idea: I replaced the third stop light, the one on the top of the rear shelf which has two little light bulbs inside, with two LEDs. It worked fine when I replaced it couple of months ago... but I never checked it since. Could that affect the brake light warning module somehow, because LEDs have much lower resistance?

dicer

And then there is the trunk hinge wiring problem.

peterls

Any way to bypass the stop light warning module?

billydpowe

iTrader: (1)

you better read up on this "And then there is the trunk hinge wiring problem."

peterls

Thanks for trying to help, but it is not the trunk wire harness.
Yamae was right (as was my distant suspicion) - it was the "warning light module" which is in the trunk, on the driver's side next to the Pioneer amplifier.

Since I don't have a diagram or any guidance, I was forced to guess which wires to connect (whatever can be found on the net does not apply to our car - wire codes are different). At first try, I managed to have my stop lights permanently ON. So, while it did prove a point, it was a not a solution. After much trial and error, I have managed to have stop lights that are not on the trunk working properly, but no other lights (so I cannot drive at night). Obviously, this means that the warning module is connected to everything that lights up in the rear, including rear lights.

Now, it is back to testing (while hoping not to blow that 25A fuse). Once I have it all figured out I will post the results so that other Gen1 owners can do the same when their stop lights go out due to faulty warning module. So far I figured that there are four wires in total that need to be connected together for the brake lights to work. I found out three, so one more and I am done with the brake light problem. Then it will be on to the rear lights, which I am hoping should have no more than three connectors, if that. I think that brake lights use thicker gauge wire while others use thinner... we'll see.

peterls

So I figured which wires to connect, and have my brake lights and rear lights working.

But, once I fixed the brake light issue, I discovered that now my power windows don't work, the sunroof doesn't work, the instrument cluster does nothing and is pitch black (although, curiously, the fuel gauge seems to work) and remote door lock does not work either.
The stereo, HVAC and power locks work and the car is running fine so far.

Any ideas? I was hoping it would be some of those big fuses, and I still have to check them, but I have a feeling I've burned up something bigger - probably a few relays...

CELSI0R

Definitely check out all of your relays. What may have happened is, while re-wiring your module, you may have sent power directly through the system with no load, resulting in a few blown fuses/relays. Better double check and make sure.

Also, I would love to see any documentation you have about the module. I always thought there was something strange about that module, which causes the lights to act oddly sometimes.

peterls

I've checked those 30amp power window and other 30amp fuses near the brake pedal and they have very low resistence, which leads me to believe that they are fine. (besides - they are such odd shape, where would I buy a new one? Is it a Lexus OEM part?)

I'd like to check relays, but I have no idea where they are. They don't seem to be under the hood - everything there is cooling and engine related... so it seems that relays are in doors maybe?

And as for the instrument cluster, I don't have a clue what to do. I probably need a new cluster.

Any ideas? Yamae?

Yamae

I don't know much about a 90 LS400 but what I imagine is that those non working units are consisting of 2 different types of units. Those are motor units and control units. Those have different fuses each. What I assume is that the power source line for control units has a blown fuse or something similar to it. I mean a connector is not fully inserted or the cable is not well connected.

There are switches for power windows, the sunroof and the remote door lock. Those switches are connected controlling circuit boards and those boards may be getting the power separately from the motor units. The instrument cluster may be getting the power from it too. I imagine that the power line to those controlling circuit is not well connected. So what I suggest you is to find that line and check the voltage.

PS: The name of the fuse is called "10A Gauge" for the Gen2. Probably the same for Gen1. The fuse "10A Gauge" feeds +12V to the cluster, door lock, tail/brake light warning circuit and others.

peterls

Thank you Yamae and all others.
So, for those who are following this saga:
Today I decided to finally figure out what was going on. As is always the case with me, I started with all the unlikely things first: the relays, circuit breakers, wires, ecu, reset everything by disconnecting the battery for a few minutes... and of course, none of it worked.
Then I decided to inspect ALL fuses, regardless of what they are for, all over again, but this time with a strong flashlight (one of those 30 LEDs lights that are really bright). And one fuse was out, which I somehow missed before - the one that is near the brake pedal, labeled 'GAUGE'.

That one 15amp fuse controls the instrument cluster, windows, sunroof, and probably a few other things. I replaced it and everything was working normally again.

Now, I still have not finished figuring out exactly which wire controls what in the rear lights warning sensor connector wires. I have the brake lights and rear lights working by connecting them, however, I haven't figured out which connector is for the brake lights on the trunk. So I have only the brake lights on the sides and the third one that's in the middle, but the two on the trunk are not working - legal but not the way it is normally on this car. When I figure that out too, I will post the diagram here so that anyone with a 1st gen LS400 can bypass the brake/rear light warning module.

Yamae

I hope the link below may help you some.
https://www.clublexus.com/forums/ls-...-pictures.html

Anyway, congratulations on your finding of the open fuse. My assumption was partly right but I now understand that the Gen1 has a 15A fuse for the gauge and related other control circuits.

peterls

Thanks! What threw me off was that there is a fuse for "power doors" and that one was ok. And there were no fuses for power windows or sunroof, so I thought it must be a relay or a breaker or something... never thought that "gauge" meant "windows"

And yes - you were right. It helped to read your reply because after checking all those things you mentioned (like every connector and so on), I figured - "let's check every single fuse again", and that worked.