the parking brake wire on my 92 VR4 was gray not purple. It runs along the center console on the driverside. Take off the carpeting and it should be in plain view. As for the RPM wire, im not sure what year you have so it could be in a few places. If your a 91-93 it should be pin 101, if your a 94-97 then its pin 58, a 96-97 is pin 51 and 98-99 is pin 45. I'm looking for the diagram that will help you out a little more, ill post it if i find it. Hope that helps.
Just make sure you get the RIGHT wire going to the ECU for the rpms. I didn't have the right one originally for my MPH sensor line, haha. Was tapping into something for the air conditioner I believe, woops. Lucky for me, it didn't cause anything to blow up.
The difference is that the purple wire controls the switch on/off for the unit. When your car is on with the turbo timer, if you put the ebrake down (disengage it) the car will shut off. This prevents someone from braking in and steeling the car while it is still on. If you ground out the purple wire then the car will not turn off when the ebrake is disengaged so you would be able to drive the car while the TT is still shuting down the car.
Hope That helped
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