Wiring diagram - advice please (photos)

[marinabrian]

Here is the cruise switch overview, showing the two separate switch states used for the brake lights and the cruise control






Now you've no idea how difficult this was to photograph, as the time differential between the two switches actuating is almost instantaneous.



Normally you would see either this.......




Or indeed this......




Brian

[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.

[SD1too]

Originally Posted by goltho

...the other GP earth "feed" from pin 4 is earthing when it shouldn't.

That's not what Jamie has said Dougie. Look here ....

Originally Posted by Jamiewelch

... the brake switch says it is constantly pressed and the brake light test passes perfectly fine ...

As I understand it, T4 calls terminals 1 & 3 the "brake switch" and 2 & 4 the "brake light test" (see MarinaBrian's screenshots).

Originally Posted by goltho

... I removed the feed as you suggested and cruise still doesn't work.

Good; that eliminates your new feed.

Originally Posted by goltho

The yellow IPK cruise light isn't lighting up at all ...

New question!
This is fed from the cruise ECU C0239-11 to header C0291-11>13 to the instrument pack. Do you have a voltage there? If not:

Is the tiny green LED in the cruise control on/off button illuminating?
Are you seeing +12v ignition on the cruise "relay" C0895-8?
When the on/off button is pressed, do you see +12v at C0895-12?

Simon

[goltho]

Originally Posted by SD1too

As I understand it, T4 calls terminals 1 & 3 the "brake switch" and 2 & 4 the "brake light test" (see MarinaBrian's screenshots).

Noted, thanks.

Originally Posted by SD1too

New question!
This [IPK light] is fed from the cruise ECU C0239-11 to header C0291-11>13 to the instrument pack.

Well it isn't actually because C0291 on my car has pins 11-14 missing. I therefore added the missing EAT C0932-49 brown wire and split-connected C239-11 and the light C0230-5 to that. The pump C0228-5 splits from the joint at the IPK light. That was how I worked around not using header C0291.

I do not however have a voltage on any of these points. I'm wondering though if the set/accelerate switch on the wheel needs to be pressed before voltage is present? That's what brings my CDTi IPK light on. Having said that, the IPK light here still doesn't come on under any circumstances.

Originally Posted by SD1too

Is the tiny green LED in the cruise control on/off button illuminating?

Yes

Originally Posted by SD1too

Are you seeing +12v ignition on the cruise "relay" C0895-8?

Yes

Originally Posted by SD1too

When the on/off button is pressed, do you see +12v at C0895-12?

Yes

I removed the seat and old brake switch quite easily, connected the new one, and played with the meter before trying to install it. It was a bit of a PITA and I've only gone & forgotten which way round the voltage numbers went but both pairs of pins (1-3 and 2-4) increased or decreased voltage whenever I moved the tip of the switch close to metal. I'm annoyed I didn't note the numbers but it made good sense at the time. The bad news though is that I gave up trying to refit the new switch after 45 minutes when I decided I'd had enough and really did need to clean the cuts. I've tricked my motor engineer buddy into abusing his slightly-younger body tomorrow pm so should have it done then. Seems to be working fine though as the brake lights are correctly stuck on now given the switch is dangling under the dash somewhere.

Dougie.