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Author: Subject: Pedal based switches
Slimy38

posted on 14/8/20 at 07:46 AM Reply With Quote
Pedal based switches

My Mazda donor has a clutch and brake switch mounted on the pedals. The brake is an obvious one, I think the clutch one is something to do with idling? But I'm a bit confused how they fit. They only have a couple of mm travel, but the pedal moves further than that.

Can anyone give me a quick overview on how they're intended to work? I'm using a floor mounted pedal box based on the Haynes Roadster book one.

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JAG

posted on 14/8/20 at 08:18 AM Reply With Quote
I'm guessing at the functions a little but normally....

Brake pedal switch is brake lights (as you assumed)

Clutch pedal switch is normally to control fuel cut-off on over-run

They don't need to match the switch travel to the pedal travel as the switches are just on/off. When the driver operates either pedal the switch moves from NO to NC or vice-versa.

[Edited on 14/8/20 by JAG]





Justin


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Slimy38

posted on 14/8/20 at 08:36 AM Reply With Quote
I've just found the original fitting pictures, they're fitted to the front of the pedals so they release when the pedal is pressed. I was under the assumption they were pressed when the pedal was pressed.

Time to make some brackets...

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big_wasa

posted on 14/8/20 at 09:28 AM Reply With Quote
There are lots of theories on what the clutch switch does but it's not likley to cut fuel on over run.
This would be done with speed vs tps.
The clutch switch is likley to be a load switch that ups the rpm a touch, for example when at the lights to help you prevent stalling.
Fords have other load switches like the Ac and even the heated windscreen.

The switch is likley to be normally closed so on the Ford ecu's I run that pin direct to earth eliminating the switch.

It's worth looking at a wirring diagram to check if it's a chassis earth or a shared balanced earth. But that's usually for sensors like the tps

[Edited on 14/8/20 by big_wasa]

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Slimy38

posted on 14/8/20 at 09:50 AM Reply With Quote
quote:
Originally posted by big_wasa

It's worth looking at a worrying diagram to check if it's a chassis earth or a shared balanced earth. But that's usually for sensors like the tps


OK, consider me worried, what's the difference between a chassis earth and a shared balanced earth? I was going to bolt all the black wires to the chassis, is there a need to keep some isolated?

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avagolen

posted on 14/8/20 at 10:05 AM Reply With Quote
Clutch switch could have been Cruise Control disconnect and
some cars require clutch depression to start the engine.





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Slimy38

posted on 14/8/20 at 11:07 AM Reply With Quote
quote:
Originally posted by avagolen
Clutch switch could have been Cruise Control disconnect and
some cars require clutch depression to start the engine.


I remember the donor had no cruise control, you might be right about the start though. It's been so long since I've started it!

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big_wasa

posted on 14/8/20 at 12:06 PM Reply With Quote
quote:
Originally posted by Slimy38
quote:
Originally posted by big_wasa

It's worth looking at a worrying diagram to check if it's a chassis earth or a shared balanced earth. But that's usually for sensors like the tps


OK, consider me worried, what's the difference between a chassis earth and a shared balanced earth? I was going to bolt all the black wires to the chassis, is there a need to keep some isolated?


Oh don't you just love predictive text

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adithorp

posted on 14/8/20 at 12:54 PM Reply With Quote
quote:
Originally posted by big_wasa
There are lots of theories on what the clutch switch does but it's not likley to cut fuel on over run.
This would be done with speed vs tps...

[Edited on 14/8/20 by big_wasa]


But it probably would be needed to switch fueling back on when already in an over-run fuel cut state and the clutch pedal was depressed.





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JAG

posted on 14/8/20 at 01:40 PM Reply With Quote
quote:

Clutch pedal switch is normally to control fuel cut-off on over-run



This comment is based on my Mazda MX5 1.6 which has a clutch switch and a gearbox mounted neutral switch on the same circuit. If the circuit is not earthed then the ECU cut's fuel when the throttle is shut.

OP mentioned his engine was from a Mazda - so he may have the same set up





Justin


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Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!

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nick205

posted on 14/8/20 at 01:53 PM Reply With Quote
quote:
Originally posted by avagolen
Clutch switch could have been Cruise Control disconnect and
some cars require clutch depression to start the engine.



IIRC my VW Passats (x2 both 2007) wanted the clutch pedal pressed for engine start.

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theconrodkid

posted on 14/8/20 at 02:08 PM Reply With Quote
the clutch is for the muricans so you cant start it unless the clutch pedal is depressed, just bridge the 2 wires and bin the extra weight





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britishtrident

posted on 14/8/20 at 02:17 PM Reply With Quote
On US market cars the clutch switch will not allow the starter to activate unless the clutch is depressed --- it is wired the same as automatic transmission gear lever postion switch.
I presume for UK market it is disabled in software.

[Edited on 14/8/20 by britishtrident]





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Slimy38

posted on 14/8/20 at 02:28 PM Reply With Quote
quote:
Originally posted by JAG
quote:

Clutch pedal switch is normally to control fuel cut-off on over-run



This comment is based on my Mazda MX5 1.6 which has a clutch switch and a gearbox mounted neutral switch on the same circuit. If the circuit is not earthed then the ECU cut's fuel when the throttle is shut.

OP mentioned his engine was from a Mazda - so he may have the same set up


You're spot on, it's a 92 MX5 1.6 for me too. I got very familiar with the gearbox switch, mainly because it just seems to get in the way when getting the engine test fitted!

So if I understand you correctly, if I have;

1. Gearbox NOT in neutral.
2. Clutch pedal NOT pressed.
3. Throttle closed.

Then the ECU will cut the fuel? And in any other combination it maintains fueling?

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JAG

posted on 14/8/20 at 08:47 PM Reply With Quote
quote:

So if I understand you correctly, if I have;

1. Gearbox NOT in neutral.
2. Clutch pedal NOT pressed.
3. Throttle closed.

Then the ECU will cut the fuel? And in any other combination it maintains fueling?



Yes - that's correct. This is the engine wiring diagram...

MX5 engine wiring diagram
MX5 engine wiring diagram



The Clutch Switch and the Gearbox Neutral Switch are at the bottom of the picture in the middle

[Edited on 14/8/20 by JAG]





Justin


Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!

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