Car Analogy

Background:
Pressing the clutch to start the car means pressure on the thrust washer bearing, at a time when there is no oil pressure to it. There aren't many weak points on our superbly engineered cars, but this could potentially be considered one. Its really only an issue if you have an aftermarket pressure plate, such as the very popular Act PP. But if this bearing goes, it could take out your engine.

The workaround is to perform a clutch interlock bypass. This can easily be done with a piece of wire or even a paperclip. You unplug the two conductor clutch interlock connector, and bridge the two connectors on the harness with the bypass wire. Now the car thinks the clutch is pressed all the time, and lets you start the car without pressing the clutch, without exposing the thrust washer bearing to any stress. Which is fine, except if you let someone else drive the car or it has to have service (I do my own work, but I still gotta bring it to a place for tires and alignments). If they press the start button while the car is in gear, its going to lurch, and could strike another car or something, and you would have some liability for bypassing a safety device.

So a better approach would be to do the interlock bypass using some other switch in the car. Where you have to activate that switch instead of the pressing the clutch. The idea is if the only way the person could have the knowledge about the switch is if you explained it to them, and you would also explain about not starting the car in gear. A side advantage would be this could act as a theft deterrent as well. The switch could be something hidden you add to the car, or you could reuse an existing switch. One member here used the VCS switch for this. You have the hold down the VCS switch while starting the car. There is an excellent thread he created on this.

I decided to use the brake light switch for my bypass. Something I've been planning for a very long time, and covid gave me time to do it. This way doesn't provide any theft deterrent, but doesn't require any special instructions for someone to start the car. The idea is modern cars train people to press the brake while pressing Start. So there is a built in safety in that they either have to press the clutch (an occasional dry thrust bearing start isn't going to cause an issue), or the brake in order to start the car. If pressing brake, and car was left in gear, brake will restrain the lurch, and peoples instinct if a car moves when it wasn't expected is to mash brake harder. So safety is sorta baked in. There are arguments what interlock bypass works best, I'd prefer to keep this thread to how to do this particular type of bypass.

The clutch interlock is a simple two conductor switch. However the brake light switch is a little more complicated, as it has to allow powering the tail lights, signal the ecu, etc. So there are 4 wires to the brake light switch, and it signals by applying 12v to the output when pedal is pressed. So to perform this bypass we need to wire in a relay. Its really just 3 wires on the car to tap into, not difficult (except for the part about wiggling under dash and doing it cramped and upside down).

How to:


A typical relay used for automotive work has 5 wires, and you usually use only 4 of them, as you either use the normally open, or normally closed wire. We'll be using Normally Open, N.O.

You'll connect one relay wire to ground, you'll connect one relay wire to the brake light switch. Then two relay wires to the clutch interlock. The clutch interlock will stay plugged in, so clutch still works to start the car (with a simple paperclip bypass, you leave the clutch switch unplugged, not needed here).

Photo of relay harness, without relay plugged in yet (I did that last). Note, if you use these types of wire taps (the blue things on the wires), the tap should not be connected first as shown. Tap them into cars harness first, then after that connect the relay harness wire into the tap.



The clutch has two interlock switches, upper and lower. The one we are bypassing is the upper one, that is harder to get to. Thankfully you leave it plugged in. Trace the two wires that come from the upper switch. One Black, one Blue. Tap into these in a convenient spot, and connect the relay Yellow and Blue wires, one relay wire to the cars black wire, one to the cars Blue wire. Polarity does not matter. The Yellow and Blue wires are known as 30 and 87 in a relay pinout. These are the Normally Open switch connections. When the relay is energized, these are the wires that are switched together.

Connect the relay Black wire to ground. This is known as relay pin 85.

Connect the relay White wire to the wire on the brake switch that gets 12V when you press the brake pedal, the White wire with black stripe. Again, you can leave this connector plugged in, and just find a convenient place to tap into it. the relay white wire is known as pin 86.

When the brake pedal is pressed, 12V is going to get applied to the relay White wire, which flows through the relay coil to the Black ground wire. This engages the electromagnet, which pulls and flips the switch, to connect the relay Yellow and Blue wires. That is all a relay is, an electromagnet that pulls a switch closed. Its like a remote control switch, that is controlled by applying power to the magnet. The relay doesn't apply electrical power to the other wires, it just switches the Normally open wires closed, and the lesser used Normally Closed wires open.

The relay Red wire, pin 87a, is the Normally Closed wire, which we won't use here. It switches from closed to open to pin 30, the Blue wire. So you typically use 30 (Blue) and 87 Yellow, or 30 (Blue) and 87a (Red). We're doing 30-87, so no need for Red.

In the harness I used, it was easy to stick a jewelers screwdriver into the connector to push the release and remove the red wire from the connector. You could also cut it, or just leave red hanging.


In all, its really not a difficult wiring effort. Ground, tap one wire into brake switch, two wires into clutch switch.

Now the following methods will all start the car:

- Press clutch pedal (service guy, someone borrowing the car, etc)
- Press brake pedal (you)
- Press both clutch and brake pedal (a more careful service guy or someone borrowing the car)

If you don't press anything, car will not start. No matter which of the above you press, there is a measure of safety built in if car left in gear.

zeroptzero

I screwed a metric acorn nut on the end of the switch to keep the plunger compressed 100 percent of the time. The end of the switch is threaded, I just put on the acorn nut and zip tied it, no wiring changes.

Kyle

The whole point of this is to have safety. Anyone can screw a nut on the end of the switch or better yet, just use a paper clip as a jumper lol.

Nice DIY OP.

Live Fast

Using some Posi-taps with this would be a great way for people to easily do it. Bypassing the clutch interlock switch is a must for heavier pressure plate cars and it's nice really on any cars.

Car Analogy

Yes, wire taps such as positaps highly recommended here. That is what I used. No cutting or altering the cars wiring harnesses.