Brake Lamp Sensor signal
 

I'm fixing some wiring gremlins, including the brake lamp warning light being on. As severally of my problems were related to a damaged left side wiring harness, I would like to know if the "white/green" wire from the sensor should provide 12 volts, or tie to ground? When the system and bulbs are working properly. Right now, the light is on until I turn the lights on.
At this point I want to verify the integrity of the harness repairs, and being able to inject the correct signal is the fastest way to confirm. One of the damaged wires was the yellow 12 volt switched signal to the sensor was severed and the red/black taillight wire melted to several other conductors.
Thanks.

Hot

Thanks. Does it open if the brake lamp is bad? Or does it tie the wire to ground when the lamp goes bad?

Grounds to activate.

Unplug the connector to the sensor and start the car. The lamp should be off. If not then you have a short in the wht/grn wire or gauge assy.

So....
if I unplug the connector at the sensor and jumper the yellow and white/green wire (12 vdc to the gage assy), the light is off.
At the sensor itself I get no voltage at the white/green wire, nor is it grounded.
I would conclude, possibly wrong that my sensor is bad.
Thanks for the help.

The way you want to test doesn't tell me anything. If the key is not on and with engine running you can not test properly.

Keep it simple. DO WHAT I POSTED ABOVE.

I LOVE IT WHEN SOMEONE ASKS FOR HELP AND THEN DOESN'T FOLLOW SIMPLE DIRECTIONS WHEN GIVEN.

In general it's a bad idea to power a circuit if you are not sure where the power will end up.

Ie... It takes less than 1 volt to activate the air bag.

I probably wasn't clear in my message. With the connector at the sensor disconnected and the engine running the brake lamp indicator is lit, until I turn on the running lights. Then it goes out.
As you previously stated, the white and green wire should be hot, the yellow wire (to the sensor) is switched 12 volts and by jumpering them at the sensor the brake lamp indicator is not lit.

So you have a short in the w/g wire or gauge assy. The indicator lamp turning off is a symptom of the short not the problem itself.

The y and w/g wires jumped together shouldn't activate the lamp for 2 reasons. 1. They're both hot, hot n hot doesn't complete a circuit. 2. w/g wire or gauge is shorted. Shorted doesn't tell you if it's shorted and open.

If it's shorted and open then the lamp will be on from the short but when you give it power it will not be on. In other words the wire/circuit board melted to ground on the lamp side and leaving the rest of the wire/circuit board open on the sensor side so when you power it, it goes no where. Also that may explain why the w/g wire at the sensor is not hot.

To clearify.

1. The indicator lamp has a shot so lamp turns on when car is on.

2. Indicator lamp turns when you turn on the light switch because electricity takes the path of least resistance. In this case the lamp has more resistance than the light switch. So the indicator lamp turns off when you turn the light switch on because the path of the electricity changes from going through the lamp to going through the light switch... Path of least resistance.

Now to find the short. I haven't even looked at the wiring since the last batch of e-mails. At this point, I can remove the bulb an solve the problem.

Well, I found the short! I decided to follow the tail light wire some more up the driver side harness and just about the B pillar it was shorted to the white / green wire. I separated the wires and confirmed the presence of 12 VDC at the white / green wire, and also that my brake lamp warning bulb is no longer illuminated. After pulling it apart, and ultimately running a new wire from the fuse panel, all my electrical items (alarm, memory seats, turn and tail lights) on the harness are now working! I need to confirm I have 12 volts at the sensor, but am pretty sure that I do, and now have to decide if a salvage yard sensor is worth it.

:suite:


thanks for the follow up!