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Passenger Brake Lights Don't Work

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It's a 1994. Running lights work fine it's just when I press the brake pedal the rear passengers brake lights don't light up, driver side works fine. I checked and switched the bulbs, checked the fuses 39 and 38 switched both 15a for working ones, and checked and replaced fuse 45 which is brake light and horn, brake lamp indicator is not lighting up on dash. Im not sure what else to check at this point, any suggestions? Thanks.
 
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The likely causes are:
- there is a problem with the interconnecting plug for the passenger side brake lights
- there is a problem with the grounding connection of the passenger side brake lights
- the brake failure sensor has failed

Easy things first - check the right side tail lights. They share the same ground as the brake lights. If the right side tail lights work its not the ground connection. The left side brake lights get their power through the right side sensor module (see the diagram below). If the left side is working correctly that pretty much gaurantees that the interconnecting plug is OK; but, check the plug anyway. Make sure that the plug to the sensor module is OK. As a final test, you can by-pass the sensing element in the sensor by adding an electrical jumper from pin 4 to pins 5 and 3 on the sensing module. If the brake lights start working that pretty much confirms the sensor has 'snuffed it'.

Something is a bit off with your warning light because when the brakes are applied the warning light circuit requires a ground through the sensors to stop it from lighting up (it is supposed to be fail safe that way). Does your warning light power up when you first key on? If not, you could have two problems, right rear brake light problem and the dreaded instrument cluster capacitor failure. Don't mess with cluster problems because they have been linked to vehicle fires.

Right side brake light.jpg
 
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The likely causes are:
- there is a problem with the interconnecting plug for the passenger side brake lights
- there is a problem with the grounding connection of the passenger side brake lights
- the brake failure sensor has failed

Easy things first - check the right side tail lights. They share the same ground as the brake lights. If the right side tail lights work its not the ground connection. The left side brake lights get their power through the right side sensor module (see the diagram below). If the left side is working correctly that pretty much gaurantees that the interconnecting plug is OK; but, check the plug anyway. Make sure that the plug to the sensor module is OK. As a final test, you can by-pass the sensing element in the sensor by adding an electrical jumper from pin 4 to pins 5 and 3 on the sensing module. If the brake lights start working that pretty much confirms the sensor has 'snuffed it'.

Something is a bit off with your warning light because when the brakes are applied the warning light circuit requires a ground through the sensors to stop it from lighting up (it is supposed to be fail safe that way). Does your warning light power up when you first key on? If not, you could have two problems, right rear brake light problem and the dreaded instrument cluster capacitor failure. Don't mess with cluster problems because they have been linked to vehicle fires.

View attachment 174807

Ok so first two passes which leaves me to my third option. I don’t think I have a jumper to check those pins, but I suspect it is the brake light sensor failure. Do you know which part number is it? I have these two but not sure which one is the left and right one.

37540-SM4-003

37540-SM4-901
 
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You can depin the required terminals, make the connections, and thereby bypass the sensor.

The next thing is to replace the incandescents with LEDs. They light up significantly faster allowing more reaction time, brighter, use less energy, and a lot less heat.

To make the LED conversion complete you have to modify the flasher, easy, to prevent fast flashing.
 
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The parts manuals make no distinction; but, they are different because the right side has the internal bias diode and the left side doesn't. The 1992 ETS manual has a rather cryptic notation of black for the left side sensor and brown for the right side sensor. No explanation of what that refers to. If you go to the later 1997 ETS manual that notation is missing.
1992 ETS brake lights.jpg
If you go to Amayama's website they have actual pictures of the sensors and 901 has black lettering on it


and 003 has what looks like red lettering on it. Click on the little camera icon next to the part number to see a close up photo.

Maybe red is actually brown and that is what the black / brown refers to? Check your left and right sensors to see whether they have different color lettering and then pick the sensor that matches up with the lettering on your failed sensor. The other option is to go to the dealership parts department and ask them to figure it out. The sensor was used in more cars than just the NSX so they may have them in stock..

As an observation, the sensor is a fairly dumb-ass simple device. Looking at the pictures of the back of the sensor on the Amayama website, I am thinking solder fractures just like those that occur on the main EFI relay. Have a look and you may be able to fix the problem with a couple of minutes time and a soldering iron.
 
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Took the tail lights apart, unplugged the relay, cleaned up wiring and contacts, plugged everything back turns out it’s a loose wiring. Problem solved. Thank you to the best members, not just any members but NSX Prime members.
 
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