Wiring diagram - advice please (photos)

[goltho]

Originally Posted by SD1too

Yes, but remember that as it's a Hall effect device there are no moving parts.

Simon

Yes, true. I went out & checked pin 9 on C0286 which is the GP wire from the switch pin 4 (C0075-4). My reasoning for connecting to that header was that the switch pin 4 wire was/is inaccessible without some more surgery, and I made the assumption that it connects directly from C0775-4 to C0286-9 (9-11 are common). Pin 9 (and 10 and 11) on that header however tests as permanently earthed which will be one good reason why cruise thinks the brake pedal is pressed. The brake lamps work correctly so it's clear that my assumption was wrong, despite the diagram saying it was right.

[SD1too]

Originally Posted by goltho

Pin 9 (and 10 and 11) on that header however tests as permanently earthed ...

How did you test it Dougie?

Originally Posted by goltho

The brake lamps work correctly ..

They're triggered, via the LSM, from the same C0286 header which you say is permanently earthed. How can that be?

Simon

[goltho]

Originally Posted by SD1too

How did you test it Dougie?

With the positive meter probe on a live point and the negative probe on C0286-9/10/11. My assumption was that when the brake pedal is not depressed, the switch is open between pins 2 & 4 and therefore the earth should not be made from the LSM. It's behaving though as if the pedal was depressed if my logic is correct?

Originally Posted by SD1too

They're triggered, via the LSM, from the same C0286 header which you say is permanently earthed. How can that be?

That's my point. I don't know. I also checked the LSM switch pin 25 which shows as running to C0286 and then to C0775-4, which also made to earth. Am I wrong in believing that pressing the pedal closes the switch, completes the earth coming from the LSM, and illuminates the brake lamps?

Brian, what was shown on Jamie's screen was exactly what you've put above on the third photo although I'm now unsure whether switch 1 was on and switch 2 was off, or vice versa. I can see it's relevant so I've PMd Jamie to see if he remembers.

Dougie,

[SD1too]

Originally Posted by goltho

With the positive meter probe on a live point and the negative probe on C0286-9/10/11.

So you were measuring voltage then and to be more precise, the p.d. between the battery positive and the brake pedal switch pin 4.

The theory of the Hall effect device is that when it is subject to a magnetic field (which we're assuming corresponds to depressing the brake pedal) a low voltage is produced across its output (which we're assuming is pins 2 and 4). This suggests that it's not a zero resistance switch as shown in your wiring diagrams. This is why I am suspicious that they have been re-drawn from the original MGR drawings but Brian says that this is not the case. A further conundrum is that his document reference precedes mine!

Back to your measurement Dougie. What did you see on your voltmeter with the brake pedal in both positions?

Simon

[goltho]

Originally Posted by SD1too

So you were measuring voltage then and to be more precise, the p.d. between the battery positive and the brake pedal switch pin 4.

The theory of the Hall effect device is that when it is subject to a magnetic field (which we're assuming corresponds to depressing the brake pedal) a low voltage is produced across its output (which we're assuming is pins 2 and 4). This suggests that it's not a zero resistance switch as shown in your wiring diagrams. This is why I am suspicious that they have been re-drawn from the original MGR drawings but Brian says that this is not the case. A further conundrum is that his document reference precedes mine!

Back to your measurement Dougie. What did you see on your voltmeter with the brake pedal in both positions?

Simon

So when the ignition is on and brake pedal depressed, it shows 3.7v. When the pedal is at rest, it's 11.84v.

Dougie.

[Jamiewelch]

Originally Posted by goltho

With the positive meter probe on a live point and the negative probe on C0286-9/10/11. My assumption was that when the brake pedal is not depressed, the switch is open between pins 2 & 4 and therefore the earth should not be made from the LSM. It's behaving though as if the pedal was depressed if my logic is correct?



That's my point. I don't know. I also checked the LSM switch pin 25 which shows as running to C0286 and then to C0775-4, which also made to earth. Am I wrong in believing that pressing the pedal closes the switch, completes the earth coming from the LSM, and illuminates the brake lamps?

Brian, what was shown on Jamie's screen was exactly what you've put above on the third photo although I'm now unsure whether switch 1 was on and switch 2 was off, or vice versa. I can see it's relevant so I've PMd Jamie to see if he remembers.

Dougie,

Opposite of the third image, the brake switch says it is constantly pressed and the brake light test passes perfectly fine, I'm with Brian and think it's the switch that is causing all the headache.

[goltho]

Originally Posted by Jamiewelch

Opposite of the third image, the brake switch says it is constantly pressed and the brake light test passes perfectly fine, I'm with Brian and think it's the switch that is causing all the headache.

Thanks Jamie. I'm about to collect the new switch and will hopefully get it fitted today. I'm now at a loss though given that +12v is being supplied to the EAT C0932-43 as it always has; all I've done is piggybacked off that to the cruise relay C0895-6. I can't see how a new switch is going to change that.

Dougie.

[SD1too]

Originally Posted by Jamiewelch

... the brake switch says it is constantly pressed ..

In which case Dougie if you remove your piggybacked feed to C0895-6 (the cruise "relay"), does the fault remain? That should determine whether your addition is guilty or innocent.

Originally Posted by goltho

So when the ignition is on and brake pedal depressed, it shows 3.7v. When the pedal is at rest, it's 11.84v.

Thanks Dougie, that's very interesting and appears to correlate with the results from Jamie's T4.

Simon

[goltho]

Originally Posted by SD1too

In which case Dougie if you remove your piggybacked feed to C0895-6 (the cruise "relay"), does the fault remain? That should determine whether your addition is guilty or innocent.

I removed the feed as you suggested and cruise still doesn't work. As I don't have access to T4, I obviously can't say how it would read without the connection. It seems to me though that that GR feed from the brake switch pin 3 is doing what it's supposed to, and the other GP earth "feed" from pin 4 is earthing when it shouldn't.

I'm only getting one (DME) error on TOAF now which I can't see to identify and which appeared after the T4 session. There are no LCM or IKE errors now. The yellow IPK cruise light isn't lighting up at all at any speed but the paddles tested ok on T4.

Originally Posted by SD1too

Thanks Dougie, that's very interesting and appears to correlate with the results from Jamie's T4.

I'll take your word for it. Just about to remove the driver's seat and attack the switch.

Dougie.