WDoherty

The small (brighter filament ) on the outer left brake light is not working. The dimmer taillight filament comes on in the 1157 bulb, but the taillight filament goes out when the parking lights are on when the brake lights are applied. The same bulb on the right housing lights both filaments, whereas the right side lights none in the this scenario. Also the left light tailight filament comes on when the brakes are applied, but only when the lights are off.

I've tested the green wire on the left side with a multimeter and it is not getting voltage on that side to illuminate the outer brake light. The inner brake light works fine, which feeds off the green/white wire. The green wire on the right taillight housing is getting voltage along with the green/white wire when braking is applied.

In short the brake signal voltage is being sent through the green wire to the right housing, but not the left housing.
Suggestions?

WDoherty

Lastest discovery. Lexus handbook has a test for the plug that goes to the light failure sensor. Everything checked out on the harness side except for the 1 terminal did not have continuity to ground.
Also, the wire that is supposed to send power to the break light has the polarization reversed when pressing the break light.

WDoherty

Tried another tail light module with same results. Unplugged spoiler LED and now the left outer brake light works and the light goes out on the dash. Resistance in spoiler light incorrect?

vangb2

iTrader: (2)

Ok, I guess I was bored and pulled out my complex wire diagram service manual for our SC's. I have view the manual and these are the components that makes up the brake light system.

Components:
Stop Switch
Light Failure Sensor
Rear Combo Lights (your light bulb)
High mount or aka 3rd Stop Light

The stop light system is seems pretty plain and simple. From what I can see in the manual; here is how it flows:

Power from 15A fuse to "Brake Switch".
When brake is applied, it closes the brake switch loop.
Power flow from brake switch to "Light Failure Sensor"
Light failure sensor outputs power to both brake light through a splice power wire if resistance is less than light failure sensor.
If bulbs resistance is infinite on either side, power flows through Light Failure Sensor turning on dash bulb light indicator.
The 3rd brake light on spoiler is power directly from 15A fuse from brake switch. It does not flow through the Light Failure Sensor. On the other hand, the high mount light (interior 3rd brake light) does flow through the LFS if factory equipped.
Ground points- LFS+stop light bulbs share the same ground point. 3rd brake light have there own ground point.

The Verdict:
Both the brake bulb, right and left are power by a single wire spliced at junction B15 . If one side have power and the other don't, the wire may be bad.

Factory spoiler 3rd light is power by a dedicated power source. It should not have any effects on the brake bulbs, unless you have a high mount 3rd brake light which is power through the LFS.

WDoherty

vanb2,
Thanks for going through that. Yes, there must be a splice in the harness after the light failure sensor because the harness has two sets of wires running at the back of the truck vs. splicing off after hitting the first light. I've tested for continuity of the red/white wire at the sensor which runs to the brake light and its good. Also, the light usually works during the first application of brakes after car is started, but it is triggered afterwords. My health isn't with me right now, but when I'm up to it, I'm considering taping into the wire that goes to the right brake light.

vangb2

iTrader: (2)

If I were in your health condition and needed this to be fixed before a citation is handed out, I would just splice it from the working side because either way it is still power from a single source.