allerton

I checked all rear lights, no bad bulbs. Might be the sending unit. I remember that the
sending unit is located behind the driver side / rear panel for my old camry. Just wanna
make sure it is at the same location for my 98 es300 before I pull the inner panel in the trunk.

lexusk8

If the tailight warning turns on whenever you brake, then the problem is most likely the brake bulb itself, specifically the brake filament inside. There are actually 2 filaments in the brake bulb: one for when the head/tailights are on, and one for when the brake light is in operation. It's the latter one that is bad, so once you replace the bulb (for your '98, it's bulb no. 7443), the warning light won't come on anymore.

allerton

I said I checked bulbs and all work as they should. I'm suspecting the
light failure sensor box itself.

intrmsof2

If you've ruled out the bulbs, check all your ground wires before you replace the box. A loose or corroded ground could easily cause your problem too.

allerton

Can you give more details, like what/where grounds to check?

ari07

You're not alone, I've got the same problem. 97 ES

intrmsof2

yeah, lemme look at some wiring diagrams.

while i'm doing that, you can just look and check any wire that's bolted directly to the chassis. Make sure none are broken/loose/corroded. If you already know where the sending unit is, try tracing the wires coming out of it, one of them has to be ground.

intrmsof2

I can't find a diagram of that circuit in my stuff. i think I had one, but I guess I lost it. My previous suggestion should still pertain though; if you know where the box is, just trace all the wires and check all the connections. Corrosion and loose connections are your most common electrical enemy.

allerton

Thank you all guys. Here is my update:

I replaced all stop lights first ( 3 of them ). Then I found that the rear light failure warning light won't come on if the light switch was not on. If turn the switch on either first or second position, then the warning light would continue to come on whenever I step on the brake. So I went on to change another two rear lights ( on the trunk lid ), to my surprise, these two are not matching, one was W5W(#2825) and the other was #194. I think the W5W was the right bulb, but the #194 was a wrong one to put there.

Now the annoying warning light is gone... though I still don't know why