AlaskanLS

I had lamp failure light on for years, I read multiple threads to find the cause of lamp failure light on but no success, my problem was not in the wiring loom or burnt brake light in the middle. All my bulbs were functional but I still replaced them with brand new one but it didn't fix my problem.
Many weeks ago I saw one of the brake light in the back wasn't as bright as the rest but I thought maybe the lens is dirty and that's why it's not bright as the other brake lights. Today I read about voltage drop on the internet and I decided to do voltage drop test on the brake light that wasn't bright as other lights and guess what I found? That dim brake light wasn't grounded properly as soon I fixed the problem, I decided to check the brightness and it turned bright like the other lights. Lamp failure light also turned off on instrument cluster.
I also checked the FSM and was about to test the sensor itself but sensor turned out to be functional. Here is a copy of lamp failure sensor diagnostics.

213374U

Fantastic post, thanks for sharing!

CELSI0R

Very nice, AlaskanLS! I had the same problem as you with one of the outer tail lamp bulbs on a 91. Only one of the two filaments worked, despite having changed all of the bulbs and running multiple tests with the Tail Lamp Failure module. It turned out to be a bad ground in the socket itself, when the car was manufactured.

I documented my fix here:
https://www.clublexus.com/forums/ls-...l#post10163098