Parking brake switch wire goes where?

[rainei]

So I've got a 91 NSX that used to have an aftermarket Double DIN, and I'm in the process of removing that and all the speakers as well as all the accompanying wiring. As the aftermarket head units require the parking brake to be up to play videos, I've got a spliced wire into the parking brake switch. However, that entire connector is all chopped up, and I have no idea where the green/yellow wire is supposed to run to.

The parking brake switch seems to be working pretty well, and I've got continuity on the green wire, so it appears all I need to do is connect that to wherever the green/yellow wire used to go.. I did some searching, and apparently I should be looking for a green/red wire somewhere..

I had run the car without the headunit and everything was working fine, but it was no longer fine after removing all the other speakers and speaker wiring..
And seeing as how the reverse lockout switch (6 speed swap) is wired to the parking brake, getting this switch back to where it belongs is pretty important.

Any help or advice is greatly appreciated!

View attachment 159652

 

[Old Guy]

First observation.

On an NSX originally equipped with a 6 speed transmission, the reverse lockout system has no connection to the parking brake switch. The reverse lockout system is controlled by the ECU which controls a relay which operates the reverse lockout solenoid which blocks shifting into reverse if the speed is above 19 km/h. I am guessing that you don't have the later ECU (unless you also changed the engine) so you lack that control input. As an observation, the reverse lockout only 'locks out' when the solenoid is energized. If you don't wire up the solenoid, the lockout should never lock out leaving you free to shift into reverse whenever you want. You could connect the reverse lockout relay (which controls the solenoid) to the parking brake switch which would then prevent you from shifting into reverse unless the parking brake was applied - that would be a really annoying feature. Since you have a hybridized car you will need to figure out how the reverse lockout solenoid was connected; but, in a normal 6 speed NSX the solenoid is not controlled by the parking brake switch.

The grn/yel wire from the parking brake goes directly to connector C451 which is a 20 pin junction connector (matching male and female connectors - not a connector that plugs into something). Now for the really bad news. C451 is located up fairly high behind the dashboard on the right side of the car. It is perhaps 10 - 15 cm above where the door lock and security modules are located. On a 1991 which does not have a passenger air bag, you might be able to see the connector since it appears that your glove box is out and it might be accessible. I think to physically access the connector on my 2000 NSX you may have to remove the dash. From connector C451 the grn/yel wire goes to 18 pin connector C450 which is located upper center close to the sunlight sensor (definitely requires removal of dash to access. When it comes out the other side of C450 it turns to grn/red. So, the short answer is that unless you are prepared to remove the dash, do not bother to go looking for the grn/red wire.

I think your best bet is to go looking for the end of the original grn/yel wire which connected to the parking brake switch. The route of the grn/yel wire to connector C451 is convoluted. In this diagram from the 1991 manual (which you can find on the web), C505 is the connector on the parking brake switch. You can roughly see how it enters the center harness and heads up behind the passenger area.

View attachment 159662

The harness then runs along the passenger side of the car then up behind the right passenger kick panel into the upper dash area and then heads across to the driver side behind the dash. It looks like the green/yel wire emerges from the harness as it passes by connector C451.

If you can't find the grn/yel wire where it enters that smaller center console harness I would be inclined to stop looking because it gets really painful and risky to start messing with the much larger harness that runs along the right side of the floor.

 

[rainei]

Many thanks, Old guy. I was not aware the service manual had diagrams for the connectors! I never looked that deep into it I guess haha.

Armed with the knowledge of where it is supposed to connect to, I looked down into the handbrake area and luckily found the grn/yel wire hiding under the handbrake hardware. A quick inline splice later and the brake warning light works as normal again! As for the reverse lockout, it was previously wired to the handbrake. One click to activate the brake warning light, and it will allow the shift to reverse. Now I did a quick test, and it does allow the reverse shift, but I haven't had it lock me out yet. I'm not sure if I have to have forward speed for it to reactivate, but I haven't been able to go for a test drive. I won't be able to fully test it out until much later, so this will do for now.

On a related note, the grn/yel wire was wired to a some sort of relay under the rear speaker box/trim. I can't seem to find it in the manual, so I'm not sure what it is.. The red was wired to the front head unit connector, the black to the handbrake, and the greens seem to run up to the interior dimmer relay behind the drivers left shoulder. Hopefully having it disconnected won't affect any non audio equipment..

Thanks again!

 

[drew]

You may consider wiring the lock out to the brake pedal.

 

[Old Guy]

Using the brake switch seems like a much more convenient solution that the parking brake switch. However, it will require a change in the way that the lockout relay is connected. The parking brake switch completes a ground path when the switch is closed. I am guessing that the OP has the lockout relay set up to have the lock out relay coil powered up by completing a ground connection for the coil through the parking brake switch. The brake switch is the opposite arrangement of the parking brake switch. When the pedal is pressed the switch closes and it applies 12 v to the brake light circuits. The OP would need to change the coil connection arrangement for his lockout relay.