Disco 2 Auto reverse lights

Hello folks, I've searched the diagrams and I can't for the life of me find what I'm looking for. I need to pick up a trigger for a relay to operate my reverse lights. There's a feed comes from the reverse led on the selector. If I could find out which wire it is I could tap into that
My XYZ switch is faulty and isn't bringing my reverse lights on. I've checked the wiring and it's OK. I know there is a fix where a relay is wired in to bypass the reverse side of the switch but I can't figure out what wire to tap into. Can anyone help me out

Might be wise to replace xyz switch before you're not driving anywhere?
Sorry don't know the work around but I imagine someone will be able to help soon.

Davidmac said:

My XYZ switch is faulty and isn't bringing my reverse lights on.

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Hi. As long as it drives in reverse and you see the selection on the dash it's not the XYZ switch cos the output for reverse lights is on the same wire with the "reverse gear selected" input to the BCU so you should double check the circuit, a common point where corrosion can affect contacts is in C0102/0484 check the continuity from there to the clusters and to the switch output, should be pin 11 green/brown wire, you should get +12V on it when reverse is selected if you dont the problem is before that plug where the signal splits to BCU, header C0294( see electrical library-connector views)... you said you checked the diagram but do you know how to read it?

sierrafery said:

Hi. As long as it drives in reverse and you see the selection on the dash it's not the XYZ switch cos the output for reverse lights is on the same wire with the "reverse gear selected" input to the BCU so you should double check the circuit, a common point where corrosion can affect contacts is in C0102/0484 check the continuity from there to the clusters and to the switch output, should be pin 11 green/brown wire
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Thank you for replying. I have power going in to the switch but nothing coming out when in reverse. Rear wiper isn’t working either but I will check that out. On a side note do you know what wire the output for the reverse led comes out on

Do you see the R on the dash in reverse?

Davidmac said:

I have power going in to the switch but nothing coming out when in reverse.... On a side note do you know what wire the output for the reverse led comes out on

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Please tell me how do you know that nothing comes out from the switch in reverse when you seem to not know which wire is that?

To clarify what i said: the R light on the selector and dash indication are both controlled by the BCU and that "reverse selected" input to the BCU comes out from the XYZ switch on a single wire which splits to the reverse lamps too in C0294(i was editing my first reply while you quoted it before that, read it again) so as long as you have selection indications working but no reverse lights the problem is between the header where the signal splits and tail lamps... i want to help you but i can't explain better

sierrafery said:

Please tell me how do you know that nothing comes out from the switch in reverse when you seem to not know which wire is that?

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I have continuity between pin 11 on CO102 and the cluster. It looks really clean in there as well with no signs of corrosion. Connector C0668 at the handbrake has power on pin 1 but nothing on pin 2 with reverse selected. The wire that I'm looking for is the one that brings the red led indicator on for reverse. That wire would act as a trigger for a relay

Anaconda said:

Might be wise to replace xyz switch before you're not driving anywhere?
Sorry don't know the work around but I imagine someone will be able to help soon.

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I've tried another second-hand one but they tend to have the same faults. £700 odd for a new one is just out of reach for me right now

sierrafery said:

Do you see the R on the dash in reverse?

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I do

Davidmac said:

Connector C0668 at the handbrake has power on pin 1 but nothing on pin 2 with reverse selected.

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I insist that it's nothing wrong with the switch if you have selection indications. IMO you are confusing something there cos pin 2 is the feed from the fuse and pin 1 is the output from the switch for the reverse lights and BCU which splits in C0294... check continuity between 0668 -1 and tail lamps... i edited the relevant part of diagram, the green arrow is the reverse output from the switch, the split point is in the red circle(the selector indications on dash and selector are controlled by the BCU based on that input).... the red arrow is the feed to the lamps... i hope it's relevant now

I just realised that there's a mistake in the diagram as pin 1 appears as female while it is male like pin 2(being the same connector) so you have to measure in the male side of connector on the green/brown(output from the switch) and green/yellow(from fuse)... unfortunately there are all kind of mistakes in the diagrams, it's not the first i see

I

sierrafery said:

Hi. As long as it drives in reverse and you see the selection on the dash it's not the XYZ switch cos the output for reverse lights is on the same wire with the "reverse gear selected" input to the BCU so you should double check the circuit, a common point where corrosion can affect contacts is in C0102/0484 check the continuity from there to the clusters and to the switch output, should be pin 11 green/brown wire, you should get +12V on it when reverse is selected if you dont the problem is before that plug where the signal splits to BCU, header C0294( see electrical library-connector views)... you said you checked the diagram but do you know how to read it?
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Have no voltage at pin 11. There are 7 outputs from the BCU CO660 that go to C0245. These outputs correspond to the relevant indicators on the dash and on the transmission selector. Do you know how to identify which one brings the "R" led on at the transmission lever

Davidmac said:

Have no voltage at pin 11. There are 7 outputs from the BCU CO660 that go to C0245. These outputs correspond to the relevant indicators on the dash and on the transmission selector. Do you know how to identify which one brings the "R" led on at the transmission lever

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I know exactly how this works and you insist in vain with the R led, i say again, that LED is electronically switched by the BCU based on the same output from XYZ like for the tail lamps, i strongly recomend to not connect anything to it cos you can ruin the integrated circuit with the extra load on that wire... concentrate on everything i posted cos if you dont have power in pin 11 of C0484 the problem is at 0294 or between it and 0484 .... though who am i to ruin your plan so if that's what you want i can tell you that the R output is to 0245 pin 11(red/blue wire), ... provided the diagram is not wrong, just in case prepare yourself to mix up or even hurt the BCU if you connect a relay to that.

sierrafery said:

I insist that it's nothing wrong with the switch if you have selection indications. IMO you are confusing something there cos pin 2 is the feed from the fuse and pin 1 is the output from the switch for the reverse lights and BCU which splits in C0294... check continuity between 0668 -1 and tail lamps... i edited the relevant part of diagram, the green arrow is the reverse output from the switch, the split point is in the red circle(the selector indications on dash and selector are controlled by the BCU based on that input).... the red arrow is the feed to the lamps... i hope it's relevant now


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Yep, I've got that. When I bridge pins 1 and 2 at CO668 the reverse lamps come on. My understanding is that power goes to the XYZ via C0668 pin 1 when reverse is selected that power goes back through CO668 pin 2 and out to the BCU and the EAT where it is processed and fed back to the relevant displays. I'm missing power on pin 2 at C0668. By my understanding when reverse is selected that pin needs to go live

sierrafery said:

I know exactly how this works and you insist in vain with the R led, i say again, that LED is electronically switched by the BCU based on the same output from XYZ like for the tail lamps, i strongly recomend to not connect anything to it cos you can ruin the integrated circuit with the extra load on that wire... concentrate on everything i posted cos if you dont have power in pin 11 of C0484 the problem is at 0294 or between it and 0484 .... though who am i to ruin your plan so if that's what you want i can tell you that the R output is to 0245 pin 11(red/blue wire), ... provided the diagram is not wrong, just in case prepare yourself to mix up or even hurt the BCU if you connect a relay to that.

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Thank you for everything, I have the fire brigade on speed dial and a spare BCU to hand. It shouldn't burn too fiercely as it is torrential rain here right now and thank you again . I will double check everything as per your instructions when the weather eases up

Davidmac said:

Yep, I've got that. When I bridge pins 1 and 2 at CO668 the reverse lamps come on. My understanding is that power goes to the XYZ via C0668 pin 1 when reverse is selected that power goes back through CO668 pin 2 and out to the BCU and the EAT where it is processed and fed back to the relevant displays. I'm missing power on pin 2 at C0668. By my understanding when reverse is selected that pin needs to go live

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According to the diagram 0668-2 must be live coming from fuse F25 and on pin 1 the reverse from the switch... from there it goes to 0294 where it splits to the tail lamps and BCU for indications so if you worked on the correct wires and only when you bridge pins 1 and 2 the lamps are coming on i'm totally confused and all i can think is that the diagram is wrong or i am missing something... good luck

sierrafery said:

According to the diagram 0668-2 must be live coming from fuse F25 and on pin 1 the reverse from the switch... from there it goes to 0294 where it splits to the tail lamps and BCU for indications so if you worked on the correct wires and only when you bridge pins 1 and 2 the lamps are coming on i'm totally confused and all i can think is that the diagram is wrong or i am missing something... good luck

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I suspect the diagrams could be wrong as I believe that they have been wrong in the past. I will leave the wiring alone that goes to C0245 and just put the relay on a switch for the short term. I'm a full time carer for my 82 year old mum who has advanced dementia so finances are limited and will stay that way until I get back to work. At that point I will fix it properly so thank you again for all your help, I really do appreciate it

This oddidity eats my mind so i'm trying to find an explanation supposing that the diagram is not wrong. When you get to it try something: let it in neutral and bridge again the pins which are activating the reverse lamps but watch if the R led and dash indication are coming on too cos if they do means that the diagram is good and problem is still in the XYZ switch as the contact is weak and the bulb's load drops the voltage on that wire but the BCU is still detecting some low voltage which is enough to trigger the indications but not the lights, i double checked everything i knew about this circuit and all the information is the same that it's a single reverse wire from the switch which splits between the BCU and lamps(and SLABS or ACE if fitted) i checked ALL the related diagrams and i doubt that all are wrong and if it's so i apologize and i retract my statement that it's not the switch at fault even though it contradics all logic but at least if it's that i've learned something new. The diagram of C0294 is relevant as well, the red arrow points toward the header where the reverse lamps are connected

edited