Clutch switch bypass switch

[Ryan]

Does that not feed the neutral switch 12v?

The relay coil is the load that allows you to do this.

And what about feeding the 12v into the gnd input on the ecm?

[PoisonDrop]

And to address the previous two posts... whats the difference if it goes from 12v - n switch - gnd or 12v - n switch - relay -gnd. Same shiz. too much current either way.

Because 12v - n switch - gnd = fire.

Keep the neutral switch all ground and you can leave it connected to the ECM.

[Ryan]

Sorry, I was assuming the relay coil load was insignificant.

[Inodoro Pereyra]

Anyways, your circuit doesn't work. You're loading the ECU input with the relay coil (don't try it, you could fry the ECU), and at the same time your neutral switch is loosing the ground reference.

You're looking at it the wrong way. The ECM input (from the neutral switch) is grounded through the neutral switch, not the other way around. Essentially, you're loading the neutral switch with the relay, not the ECM. And the neutral switch is mechanical, so you should be fine there.

So you're loading a switch?
Is the switch providing the power to drive the relay? Really?
Even is the ECU input is DC isolated (which I doubt), if you put a relay like Ryan drew you're inserting a RESISTANCE in a circuit that should give a ground reference. Best case scenario, it will make that input unstable, and probably introduce electrical noise to it, which could drive the CPU crazy. Either way, the relay will never activate.

You guys are reading way too much into this. Here's what you should do:

First off, put your tranny in neutral and test the ECM wire coming from the neutral switch for continuity to ground. Just to make sure. If you are concerned about the ECM, you can pull that pin while you're testing, but you should be fine.

On the relay, hook 85 to the neutral switch ECM wire, 86 to one side of your button, 87 to one side of the starter interlock switch (on the clutch pedal), and 30 to the other side of the starter interlock switch. Connect the other side of your button to a constant 12v source. This should get you exactly what you want.

Sorry I can't draw a picture, but I'm not really set up to scan and upload stuff from this computer. If you'd like, I could e-mail you a diagram...

I will also tell you that if you do what I described, it will NOT click every time you press the clutch.

Ryan: if you do this you will be feeding +12V through the relay coil to the ECU input. DO NOT DO THAT.

Poisondrop: nobody said the relay would click when the clutch pedal was depressed. The relay will click every time the transmission goes past neutral.

[Ryan]

Does that not feed the neutral switch 12v?

The relay coil is the load that allows you to do this.

And what about feeding the 12v into the gnd input on the ecm?

I hate to quote myself, but its twice now you've missed details that have been mentioned before....

[Inodoro Pereyra]

What I'm trying to tell you is that the ECM does NOT provide 12v to the neutral switch. If you do what your diagram says, and hook up 12v to it you WILL kill your neutral switch. I have done this before and I still do not have a neutral switch.

Who did ever say the ECU would provide the +12V?
And what part of "the neutral switch has to be disconnected from the ground" did you not understand?

[Inodoro Pereyra]

Ryan: if you feed +12V to the ECU input like poisondrop suggested, you will most likely fry your ECU. Digital inputs are normally high impedance, and they will not tolerate to be fed more than twice the ECU voltage through a resistance that, at the most, will be 150 ohms. For the input that will be like a short circuit.
The circuit I drew will work. Just make sure you disconnect the neutral switch and reconnect it as the diagram shows: one pin to +12V, and the other one to one of the coil terminals. The other coil terminal goes to ground.

[Ryan]

But then the neutral switch loses its original function. I don't like that.

[Ryan]

This is PoisonDrop's diagram. excuse the crappy quality




I now think you're arguing the same thing.


Either way, in both of your circuits the neutral switch loses its original function.

[PoisonDrop]

Now that I look at it, the neutral switch should still be connected to the ECU, I just missed a lead.

[Ryan]

howso...? If you involve 12v with the neutral switch anywhere, as I understand it, it will toast the ECM.

[Inodoro Pereyra]

The neutral switch does the same, but it's does it through the relay. It's the only way.
If you do what poisondrop suggested, you will be buying a new ECU soon...
The moment you press the bypass switch, if the tranny is not in neutral, you will be feeding +12V to the ECU input.

[Ryan]

Boom. I suddenly understand. There are three circuits in this relay. Tada!

Now I get it.

the 12v- n switch - coil - gnd is the trigger circuit to close a subsititute neutral switch circuit (resistances should be matched, lets just hope the coil isn't more than the neutral switch), and the power circuit for the button.

I'll measure the voltage applied by the ECM, and match the voltage drop over the neutral switch with the coil involved, and try and match it.

also, add a resistor matching the value of the neutral switch for the new ECM circuit, just in case.

[Inodoro Pereyra]

Bingo!
Just make sure the coil's resistance isn't less than about 100 ohms, and you should be ok.

[PoisonDrop]

howso...? If you involve 12v with the neutral switch anywhere, as I understand it, it will toast the ECM.

If you involve 12v without a load it will be like touching 12v directly to ground. With the added load of the relay it acts like a regular circuit. The neutral switch is just shares a ground point for that circuit.