Gauges not working (MK2)

[Siebrand]

Hello all!

Long time reader, first time poster here.
Never thought I'd see the day that I'd post something on a forum, but might be useful!

Right, so. As the title implies, all of my gauges have stopped working completely.
Except for the fuel gauge, which is always jumping to Full even if it's really not.

I have a little step-by-step plan to troubleshoot this issue.

First up, cleaning the connectors and contacts on the back of the cluster. Already took the entire thing out and removed it from it's plastic shell (kinda looks like an early 80's computer casing haha!)
If that doesn't work, I'll check the fuses again and I'll also check the relays. Not sure which one it is yet, but maybe someone here can show me!

After that, earthing points. Now this is the reason I'm posting here.
Because I have absolutely NO idea where these points are. I've found one on the right side of the engine bay, connected to some blue plastic box?
But that one looks fine to me and I doubt it's connected to the gauge cluster.

Let me know if you know where these earthing points are or if you have any other ideas on this issue!
Thanks!

[David]

Firstly, is your car a Mk1 or Mk2?

My first suspect would be the fuses, I can’t remember which one off the top of my head, so check them all!

Secondly, is the heater blower fan or the indicators working? If it’s a mk2 car, then they’re on the same circuit as the gauges, So if that’s a yes to both, then look somewhere else.

There’s an earth underneath the left front seat, it’d be worth checking anyway, but I don’t think anything behind the dash earths there. From what I remember, there’s another earth behind the dash on the LH side (behind the glovebox on a RHD model), that all the dash wiring goes to, if nothing else works, then find it & have a look. Failing that, there’s another earth underneath the steering wheel shroud which 2 plugs connect into; the interior lights & a few other things earth here, so again, if in doubt, pull it all off & have a look.

Otherwise, check your ignition switch contacts. There are actually 4 circuits in it, one for the ignition, two for accessories & one for the starter. Check to ensure all 4 are working. I can’t remember which way it’s wired, but when the key is in position 2, 7 of the 8 wires should have 12v running through them.

Have a look & let us know what you find.

Hope that helps.

[Siebrand]

So I’ve checked the fuses and they’re all good.
Cleaned up the contacts. Hoping that’ll do the trick.
Can’t seem to find the earthing points at all. Do you have a picture of where they are located?

[Jaba]

Dash earth points are on the steering column support under the shroud somewhere. Not sure where exactly on a LHD car. The other earth point is in the engine bay on the inner wing between the battery and the bulkhead.
You can test by providing an earth direct to the dash. The instruments which have a sensor on the engine are earthed through the sensor to the engine so nothing to check there except for 12v present.
What about the warning lights. Do they come on when you switch on before starting.

[Siebrand]

Yeah, all the lights work just fine.

[David]

Have you got a picture of your instrument panel? If you upload it, with the ignition on but the engine not running, it might give a bit more insight on what is wrong.

Have you dismantled any of the dash to look for the earthing points?

Also, I’ve just noticed above that it mentions it being a LHD? In which case, I’m not sure where the earths would be, but I’d assume I’m similar places, so under the drivers seat, under the steering shroud & maybe behind the dash on the LH side?

Also, to add to what Jaba said; there are 3 wires that go to the water & oil temp clocks; live, neutral & sensor neutral. The fuel gauge has 3 wires, but I’ve never traced them back to see what they do or where they go, but the sender units are prone to failing.
The oil level clock is more complicated, if it’s a combined pressure & level clock, it’s more complicated still; it is earthed on the back of the PCB on the instrument panel, & it has a pressure sensor neutral that it picks up from the PCB. It then has ignition live that connects to a white plug on the back of a separate circuit board & it has 2 more wires in the same board that go to the oil level sensor. Both these boards & the level sensors are prone to failing, the board can cause erratic or no readings, whereas a faulty sensor will show it to be always full. It may also fail to switch over so either never show the pressure or level (or both). There is no reason why this failing would cause everything else to fail though.

The oil pressure sensors, oil & water temp sensors, as far as I’m aware, are usually quite reliable.

Hope that helps.

[Siebrand]

Hey David, not sure what you mean by ‘shroud’.
These UK terms are always a bit of mystery for me haha!

Also quick little side rant: The mileage counter stopped working too, and as I’ve found out yesterday, it’s required to work to pass the Belgian MOT. So that’s 40 minutes of driving and another 15 euros down the drain. Again.

[Siebrand]

Update time!

Took the BX to a Citroën garage one town over, they work on old models a lot (even as far back as pre-war Citroëns!)
Turns out that the speedo cable had come loose completely, ordered a new one and had it installed.
Both the speedo and the mileage counter work again. The diesel gauge probably works and it's likely that the sender unit/floater is just busted or bent. Thus causing it to read a full tank even when it's not full.

The rev counter's sensor is definetely busted though. As for the oil pressure/level gauge, I have no idea wether it works or not and frankly I don't care.
I'll keep you lot posted!

P.S. The BX passed the inspection and is ready to be registered as an Oldtimer here in Belgium now!

[panky]

Good result - mostly