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Author Topic: Brake/Tail Light Sensor Questions  (Read 604 times)

Offline rednucleus

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Brake/Tail Light Sensor Questions
« on: 04:54:30 PM / 27-Mar-22 »
Good day; referencing my 85 hatch. I was getting the right side dash bulb warning light when applying brakes.  Checked & found I had no brake lights. Bulbs were still good so figured it was the sensor. PIA to get to under the right rear trim panel. Unplugged it, plugged back in and brake lights work again. Then they quit again, tapped the sensor and lights back on! Tried the FSM meter test; didn't meter as book showed despite working again.  BTW tail lights worked fine the entire time. My understanding is this sensor monitors both tails and brakes.
Anybody ever try to open up a sensor to see what makes them go or fix one? I am not finding a listing for one anywhere; I assume this is a years ago discontinued dinosaur.
Thanks, Red

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Offline weitrhino

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Re: Brake/Tail Light Sensor Questions
« Reply #1 on: 05:46:05 PM / 29-Mar-22 »
I've never taken one apart but that wouldn't stop me if I were having trouble with it. Unfortunately the wiring diagram simply shows this sensor as a box giving no indication of what's inside. I'm guessing the sensor looks for the presence of 12vdc AFTER each bulb, i.e. current running to ground. If a bulb is out then there would be no current present on the ground side so the sensor shunts 12vdc to the warning lamp circuit.

That's just a guess, but it seems logical.

Offline rednucleus

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Re: Brake/Tail Light Sensor Questions
« Reply #2 on: 09:19:54 PM / 29-Mar-22 »
Thinking there's some sort of mechanical contacts involved. Since plugging sensor back in, problem has recurred three times. I wedge a stick on the brake pedal and tap the sensor and the lights start working again. Was thinking about spraying some DeOxit into it thru the connector socket and see if it frees something up.

Offline weitrhino

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Re: Brake/Tail Light Sensor Questions
« Reply #3 on: 01:06:58 PM / 30-Mar-22 »
If it's electro-mechanical then DeOxit is probably a good idea. If you get inside of it I'd appreciate seeing a picture.

Offline rednucleus

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Re: Brake/Tail Light Sensor Questions
« Reply #4 on: 04:08:05 PM / 30-Mar-22 »
I am not going to open it unless it completely fails. If I ruin it opening it then I will have to re-wire the rear lights; no time, no ambition!

Offline rednucleus

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Re: Brake/Tail Light Sensor Questions
« Reply #5 on: 10:53:23 PM / 22-May-22 »
Tapping no longer makes it go so I opened it. The end where it plugs in snaps off and the circuit board slides right out. Unfortunately, no moving parts to clean. A bunch of tiny resistors, half dozen capacitors, a chip and I think a transistor.  Anyone know if we can post pics here yet? My next step will be to refresh all the solderconnections. that revived my ECU several years ago and still running great.

Offline weitrhino

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Re: Brake/Tail Light Sensor Questions
« Reply #6 on: 12:08:47 PM / 23-May-22 »
I host pics on Imgur and link them here. Clumsy, but it works just like Photobucket used to do.

Offline rednucleus

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Re: Brake/Tail Light Sensor Questions
« Reply #7 on: 10:46:18 PM / 26-May-22 »
After closer inspection, I found a loose solder joint where one of the connector pins joins the board. Hit it with the solder iron and working again.
Rodney, sent you pics via your email.  If you can post them here, that would be appreciated.
« Last Edit: 10:46:41 PM / 26-May-22 by rednucleus »

Offline weitrhino

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Re: Brake/Tail Light Sensor Questions
« Reply #8 on: 03:42:07 PM / 29-May-22 »
Rednucleus shared these pics with me so I'm adding them to the thread for him.


Here's what the component side of the small circuit board in the brake sensor module looks like:




Here's the trace side:




And here's what Red's careful eye spotted on the board; a solder joint in need of a reflow.

« Last Edit: 03:42:39 PM / 29-May-22 by weitrhino »

Offline kelso840

Re: Brake/Tail Light Sensor Questions
« Reply #9 on: 04:28:52 PM / 29-May-22 »
Good eye. Spot of solder and you'll be good for another 30+ years!
Infrequently driving an s12.

Offline rednucleus

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Re: Brake/Tail Light Sensor Questions
« Reply #10 on: 05:25:35 PM / 29-May-22 »
Thanks for posting those kind sir!!