Wiring diagram - advice please (photos)

[goltho]

I've put on a few posts recently with similar questions. Ignore them all. This is the Final Question to complete my cruise control retrofit. Jamie Welch handsomely configured my ZT with T4 this morning - thanks again. I got a clean bill of wiring health but there is a brake switch conundrum preventing it from working which I need someone's knowledge about. Please refer to the two diagrams in conjunction with the issue.

Context
• My KV6 was built without cruise and interlock
• The brake switch has all four wires connected
• Header C0285 is missing from the car. That mostly makes sense as it deals with cruise and parking sensors, none of which my car has
• The green/red (GR) wire from the brake switch pin 3 (C0775-3) is connected to the electronic auto transmission (EAT) pin 43 (C0932-43) in line with its pre-cruise state. It currently functions exactly the same as the wire from C0775-4 which controls the brakes lights i.e. power appears when the brake pedal is depressed. I do not know if it would function this way if the car was OEM-fitted with cruise as there may be two switch types (one is referred to at Rimmers as double pole, and is shown (only once) on a RAVE wiring diagram as double pole).
• Whilst T4 confirms the brake lights functioning correctly from C0775-4, it however reports the brakes being permanently on based on C0775-3. This is despite both pins C0775-3 and -4 behaving identically. This alone appears to be preventing cruise from working.
• Pin 6 on the cruise control relay (C0895-6) requires to be connected to C0775-3; in the absence of header C0285, I piggybacked off the EAT C0932-43 as above, to C0895-6. The GR wire colours are also consistent. I am however now doubting whether this is correct based on the attached diagrams.

Wot I need help with
• I do not know if the OEM brake switch is double-pole. It's only shown once in the entire ZT wiring diagrams as being double-pole and is not shown as such on the attached diagrams. Might this be making any difference to how pin 3 behaves - perhaps open when pin 4 is closed and vice versa?
• Should I disconnect the EAT C0932-43 from the brake switch C0775-3 now that cruise is fitted? I'm unable to interpret the diagram in that respect.
• Finally, the smaller of the two attached diagrams shows C0932-43 being connected twice to the missing C0285 (pin 2 and pin 3). Is it safe to assume that I can disconnect the brake switch C0775-3 from EAT C0932-43 altogether and instead connect it directly to the cruise relay C0895-6?

That's what my brain took me before I wrote this down, and it still arrives at the same point.

I realise wiring isn't everyone's bag but it's straightforward for others. I've always had a good knowledge but have limitations. Someone more qualified help will be hugely appreciated. Thanks in advance.

Dougie.

[goltho]

So this is the only reference I can find to the brake switch which shows it as a double pole unit. I'm stlll unable to determine what this means in terms of how it operates. All the evidence suggests I have a single-pole unit.

Pin 1 is from fused power
Pin 2 is to earth
Pin 3 is to cruise relay
Pin 4 is to brake lights

???

[SD1too]

Originally Posted by goltho

Now that the investigation is drawing to a close, it's worth noting that the labels for the two halves of the brake switch are incorrect in the above drawing.

MarinaBrian's T4 screenshots (post no. 31) tell us that the correct labelling is:

• Pins 1 & 3 = Brake switch 1
• Pins 2 & 4 = Brake light test switch (switch 2)

Simon

[xsport]

i have the rover 75 kv6 2.5 auto with cruise. 2001 year. mine had the original brake switch from new (dont have details as i discarded it) when my brake switch packed up last year i needed a replacement and looked at past threads and was told the xkb000022A was the only one that works now on the autos. that switch i was told would also work on the manuals. xkb000022 was only for the manual brake and clutch. whatever the truth is it worked for me no problems. same cruise and interface parts i presume. no doubt you will eventually find the right combination if not..... happy hunting !

[goltho]

I collected the replacement SCB100201 cruise interface this morning and fitted it after disconnecting the bypass wiring I successfully tried yesterday at message #82 above. There is still no voltage on C0895-9, so obviously the interface is inhibiting the 12v output to the ECU due to another element. The brake switch remains the chief suspect as previously discussed.

I removed the non-working C0895-9 feed to C0239-1 and instead of connecting a spurious 12v feed to C0239-1 as I did yesterday, I used the master switch C0749-5 output as it made sense to control everything from the same switch. Alas, instead of the IPK light coming on and cruise working as before, when I pressed the set/accelerate paddle, it flashed once and the horn sounded. Thereafter, it was dead until I stopped, switched off the engine & restarted when it repeated that behaviour.

I removed the C0749-5 supply and reconnected the separate feed to C0239-1 as per yesterday. Everything worked again. Tried the switched feed one more time but just got the flash 'n' toot followed by nothingness (presumably because the ECU errored out and did what it's supposed to do until it's restarted and cleared).

Originally Posted by SD1too

The EPC descriptions are nonsensical. Since your brake lights work and so does cruise, there's a case for cutting your losses and supplying the cruise ECU independently of the interface ECU.

The correct thing to do would be for me buy a XKB000090 brake switch and try that as it remains the only one which is specified as double pole. After weighing up the risks, disadvantages and advantages, I am not going to do so and will instead complete the wiring with the separate feed to the ECU C0239-1. I would though like to know why the cruise master switch connection produces an error as I want to have only one switch. I can work around it using a relay if necessary.

Originally Posted by xsport

...i needed a replacement and looked at past threads and was told the xkb000022A was the only one that works now on the autos... whatever the truth is it worked for me no problems

Was your car built with the wiring in place?

Dougie.

[xsport]

yes it was. just been on rimmers and they list a brake switch blue XKB000090 with the application as for cruise control but with the caveat of serial numbers from 5d345692 CP type - vin. onwards . other than that theres just the normal XKB000022A. i bet you are not relishing that brake light switch change but if your vin is in that group it could well be the one you need .

[goltho]

Originally Posted by xsport

yes it was

Your wiring will have been different to mine then, which was wired completely without any cruise elements including some headers.

Originally Posted by xsport

....rimmers ...list a brake switch blue XKB000090....from 5d345692 CP type vin onwards

Mine is prior to that but I'm sure the blue 090 would work with my reconfiguration, possibly even ironing out the last issue.

Originally Posted by xsport

i bet you are not relishing that brake light switch change

Well indeed I'm not because I'm not changing it.

Dougie.

[SD1too]

Originally Posted by goltho

... I used the master switch C0749-5 output ... Alas, instead of the IPK light coming on and cruise working as before, when I pressed the set/accelerate paddle, it flashed once and the horn sounded.

What you effectively did there Dougie was to connect the cruise ECU C0239-1 and C0239-8 pins together. I wonder if placing a diode between them would solve the problem?

You could use C0749-1 instead. That's the supply to the master switch but C0749-1 will be live only when the engine is running which is effectively the experimental state you have at the moment. However this might not work either because you'd then have C0895-8 and C0239-1 connected together!

Simon

[goltho]

Originally Posted by SD1too

What you effectively did there Dougie was to connect the cruise ECU C0239-1 and C0239-8 pins together. I wonder if placing a diode between them would solve the problem?

Yes, most likely. I'd thought of using a SPST relay triggered by C0749-5 and making a supply (maybe spliced from fuse 41 which supplies the entire cruise system) to C0239-1? Do you think it still might be susceptible though? A diode would certainly clean it up.

Originally Posted by SD1too

You could use C0749-1 instead. That's the supply to the master switch but C0749-1 will be live only when the engine is running which is effectively the experimental state you have at the moment. However this might not work either because you'd then have C0895-8 and C0239-1 connected together!

I didn't like the thought of a common connection there either.

Dougie.

[SD1too]

Originally Posted by goltho

Wot I need help with
• I do not know if the OEM brake switch is double-pole. It's only shown once in the entire ZT wiring diagrams as being double-pole and is not shown as such on the attached diagrams.

Hi Dougie,

The internal detail of the brake pedal switch in your diagrams is unofficial as far as I can tell. RAVE doesn't include it so it may or may not be correct.

Originally Posted by goltho

• Should I disconnect the EAT C0932-43 from the brake switch C0775-3 now that cruise is fitted? I'm unable to interpret the diagram in that respect.

RAVE says that C0932-43 is an input to the EAT ECU from the brake pedal switch. In other words, it tells the automatic transmission when the driver is braking. I'd say that you should not disconnect it!

Originally Posted by goltho

• ... is it again safe to assume that I can disconnect the brake switch C0775-3 from EAT C0932-43 altogether and instead connect it directly to the cruise relay C0895-6?

It appears to me as if C0775-3 needs to be connected to both the EAT ECU C0932-43 and the cruise relay C0895-6 (both are inputs from the brake pedal switch).

Simon