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Brake lamp warning bypass... what am I doing wrong?

5 December 2018
I've put a different LED high level brake light into my car as I don't have the factory rear wing, so this naturally means the Brake Lamp warning light on the dashboard comes on. I've done the bypass as per other posts on this site by connecting the white wire with green stripe to black wire (which I assume is ground) on the right side tail light as seen below, however the Brake Lamp warning light still comes on. Have I done this right?

<img src=http://www.j-spec.com.au/customers/NSX/nsx_51.jpg>


- Ben
I am completely missing something. On North American cars the high mount brake light is not directly in the brake lamp warning circuit. Only the four brake light bulbs in the tail light assembly are monitored. I believe the high mount light is indirectly in the monitoring circuit because the LEDs in the high mount light provide a path to ground which keeps the monitoring light off when the brakes are not applied.

This is the circuit for a North American LHD car.

Brake light circuit.JPG

If you want to completely defeat the brake light warning system, you need to connect the Orange/white wire from the safety indicator to ground (one of the black wires). This will hold the input to the safety indicator at zero volts and prevent the safety indicator from ever lighting up. There are better ways of accommodating the removal of the high mount brake light that would retain operation of the monitoring circuit. A stacked diode set with a cumulative Vfwd around 14 volts or a 12 v LED connected in place of the high mount brake light may provide the necessary ground path to suppress the indicator when the brakes are not pressed.

I would need to see the original posts you reference to figure out what they were doing. On first glance, connecting the white/green wire to a black wire should create a dead short on the system and blow fuse #45 in the main relay box. Of course it is also possible that the wire harness and colors are different for an RHD car so you would need to consult the RHD service manual to confirm whether the wiring is the same of different than a LHD car.
Ok, I think this is my bad. I assumed the brake lights and high level brake light were all on the same circuit, the fix that I've done here appears to disable the Brake Lamp waning light if for example you replace the regular bulbs with LED bulbs in the brake lights, but this is not necessarily related to the high level brake light. So I've done a fix here for installing LED bulbs, not replacing the high level brake light.

This thread talks about this (and some more discussion on page 2), unfortunately the images which were working a few weeks ago don't any more. I'd say I've done the fix correctly according to the photos that were there previously, but it's for a completely different problem to mine.

From everything I can tell all of this wiring at the back of the car is the same on LHD/RHD cars.

So, you believe putting something like this:
in line with the wiring to my new LED high level brake light would turn the warning light off?

- Ben
So, you believe putting something like this:
in line with the wiring to my new LED high level brake light would turn the warning light off?

No, that is a zener diode and will not work. A simple 1n4001 diode(s) in series with a resistance connected in place of the original high level brake light might do the trick. The problem is that you want to emulate the dynamic characteristics of the high level brake light to fool the brake light failure sensor into acting like the high level brake light is still connected. In order to emulate the high level brake light you would need to remove it and use a variable voltage power supply to measure its voltage versus current characteristic. I don't like pulling things apart that are not broken so I am not really inclined to do that measurement.

The brake light failure detection circuit is the same circuit for both the high level brake light and the brake lights mounted in the tail lights. It does operate slightly different for the high mount and conventional incandescent tail lights. The connection to ground as described in that post you linked will disable the brake light failure warning light in the cluster for both the high mount and tail light mounted brake lights.

I had to check the NSX Electrical Trouble Shooting manual to figure out what was going on with the white/green wire. The wiring diagram in the full service manual does not show this; but, there is a 8 pin grey plug in the back right corner of the trunk below the tail light housing. Its connector C562 and I believe the photo in post #11 of that thread you linked shows it


The orange/white wire from the safety indicator enters one side of the plug and matches up with a white /green wire on the other side of the plug. The orange/white to white/green wire is in pin position 1 of the C562 plug. This white/green wire goes directly from C562 to the right brake light failure sensor module.

From the photo in your first post, I can't tell whether you picked up the correct white/green wire. Trace the wire. If one end goes to the failure sensor module and the other end goes to connector C562 and matches up with the orange/white wire from the safety indicator then the modification that you have made should suppress the brake light failure indication. This presumes that the black wire you tapped into is a ground which is the normal practice on the NSX. Either your soldering connections are faulty or you have pulled the pins out of connector C562 or the safety indicator circuit has failed.

As a personal opinion, your method of implementing the connection to ground is poor practice. Soldering wires on a vehicle is exceedingly poor practice because aside from heat damage the solder migrates up the strands of the wire making the wire inflexible and subject to fracture because of flexing and vehicle vibration. It is also generally difficult to make a good solder joint when doing an in situ repair because of the awkward working conditions. Your connection to the white/green wire looks extremely suspect.

The modification as carried out in this photo is a much better choice.


The modification uses a dedicated connection to ground using a dedicated wire and ring terminal and does not modify the existing vehicle wiring and is easily reversible / removeable. I am no fan of the T tap connectors used in that post because they can damage wire strands if not perfectly sized and installed. There are better options for tapping; but, they require the use of crimp style fittings. The T tap is a better option than your choice of soldering.

If you confirm that you have the correct white/green wire and that the ground connection is good, then there is a problem with the monitoring circuit. Later in that post you linked @comtec takes another member through diagnosis of the monitoring circuit to find out why the modification does not work. Follow that process if your brake light failure indicator remains lit up.
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If you want to completely defeat the brake light warning system, you need to connect the Orange/white wire from the safety indicator to ground (one of the black wires).

Here's an easy way to do that. I used two of the 3M taps that you install with pliers, then made a short jumper to connect them.
tap2.jpgcircuit.jpgtap 1.jpg