Citroen XM Forum

Still raining here so I had a quick look at the early Mk1 wiring diagrams.
The mid cable speed sender box wiring only seems to be present on models with the extended RH dash display.
This speed signal goes to pin 8 of the RH display.
This type of display was unchanged for use in Mk2 cars so the signal must be the same.

John

xmexclusive wrote:Still raining here so I had a quick look at the early Mk1 wiring diagrams.
The mid cable speed sender box wiring only seems to be present on models with the extended RH dash display.
This speed signal goes to pin 8 of the RH display.
This type of display was unchanged for use in Mk2 cars so the signal must be the same.

John

That makes sense, so for petrol powered cars, with trip computer, the conversion should just be a case of fitting a new speedo head unit and ensuring it is connected.

It makes you wonder why Citroen didn't use electric speedo's from first production. Our 1988 Fiat Tipo had a digital dash, but maybe electro-mechanical devices were still in their infancy and deemed too expensive.

If this is a success, let me know John and I can help with graphics and design a clear write up if you think that would be helpful.

Hi Russ

The original XM dash display was proposed as HUD.
Just as well they went conventional for the production run as the electronics from that time proved less than reliable.
It also rapidly became non standard and difficult to replace or repair.

What state is your old car in?
Where is it?
If I need a look at a Mk1 engine bay and dash would it be suitable.

John

As John has started to describe earlier, isn't the biggest task a cosmetic one - assembling an instrument head that is S1 in appearance? Does this look possible?

Hi Chris

There is a lot more detail to the "cosmetic" work than I expected.
I have got as far as cutting out the Mk1 pcb so that it fits onto the Mk2 white shell.
I have 3 pcb tracks to repair and work out how to add the speedo connector.
There are a large amount of light baffels, channels and screens.
Need to make sure these all work correctly.
Just noticed that the two dash display top mounts are different so that is something else to check and correct if needed.
Mk2 ones are central metal studs that push into spring clips, Mk1 ones are offset drilled holes.
Can someone please check what actually fixes the top of the dash display on a Mk1.

Think I will look at modifying the spare Mk1 white frame ready for the next try.

John

Hi John,

Thanks for the latest. Looks quite a fiddly job, which hopefully will shake down into something workable.
Maybe, if the head rebuild looks a goer, we might look at having a small-and-ongoing small stock of rebuilds to meet what would probably be a trickle demand.
Alternatively, it might be that owners who would contemplate such an electronic conversion might want/be able to do their own rebuilds. A delicate bench job that requires the right bits, and tools.
Something I'd be happy to get involved with, if needed.

mk.1 are simply screwed in place.. I have a mk.1 and mk.2 display infront of me now.. the mk.2 has two smaller locating prongs at the top and are slightly further over.. the fixing lug is more central.. the pic above shows this for you.. the actualy mount is physically in the same place!

Dirty one is mk.2... other mk.1

the warning light difference on the face is only rear fog light on mk.2 in place of full beam on mk.1.. bottom right corner


Mk.1


Mk.2

Mk.1 Is a Veglia unit, Mk.2 a Jaeger .. also Mk.2 units have "Made in France" on them...

So removing the S2 Speedo head, two torx T9 at front and three T10s at rear..

I was stunned by this on this particular one..


Yes, the front peeled off in one piece!! So thats the Mk.2 Head ready...

Ok, Mk.1 speedo head out, and on this particular S1 TD unit there is no provision for the electroinc speedo, no plug and no tracks on the PCB. So, how about reverse fitting instead and fitting the S1 items into the S2 surround.. The other change between Mk.1 and Mk.2 is fuel and temperture guages swapped around! Weither this means a different pin position on the red plug I dont know. The Oil level guage never moved as this is picked up from the end GREEN Plug which is a sperate daughter board inside a mounted by pins connection.




MAJOR DISCOVERY TIME...

Removing the S2 front sticker reveals two T9 torx screws... The holes here are in the identical place to the Mk.1 speedo head!

So the fronts ARE swappable eneableing Black speedo Front onto the electronic Driver! wheres my bloody T9 torx!! Grrrrr

Thanks Paul that helps a lot.
I can just drill new holes in the Mk2 white plastic and cut off the locating pegs.
Both types of the speedo are heavily bolted into the white frame at the back.
That has decided me to use a Mk2 white frame for the conversion.
Citroen must have thought this solid fixing important so I will not try bodging a Mk1 frame.

Your last two photos clearly show the difference between Mk1 and Mk2 white frames where the speedo fits.

Hopefully I will have a test display ready later today.

John

Have you looked at tracks John? Does the Rev counter and Turbo guage ... remember TD XM have a boost guage .. use the same pick up pins?

If your not sure Ill have a look into that now

Im condident now the speedo head is swappable so we pureist can still have a black display.

Daaammm Turbo boot guage Tracks on the Mk.2 PCB are different... Thats bad news!