No light on speedo gauge and electronic speedo goes out ?

[Mr Plow]

Hi All

For some reason I have no light on my speedo gauge, I've checked the bulb, its OK. The electronic mileage reading disapears when you turn the ignition on?

Any ideas, could the two be connected?

Cheers

Liam

Edited by Mr Plow on Thursday 3rd April 20:13

[ukdj]

The backlight illumination for the gauges is daisychained between them all, assuming you have lights on the others & you haven't knocked the kill switch for the lights ?

If the bulb is ok, I'd check if you have +12v & good earth to the bulb holder, as for the electronic part of the speedo I believe there is an internal battery for this which may need replacing.

Regards

UKDJ

[Mr Plow]

Thanks for the reply.

I've done some more investigation work, it is definately not the bulb, I have tried a couple.

So..

With the ignition turned off the electronic mileage shows. As soon as you turn the ignition on the mileage dissappears, it stays off when you start the car. When you drive the car the speedo doesn't work.
If you turn the lights on, all the gauges illuminate except the speedo.

Does any one have a wiring diagram or any advice, it looks like when the ignition is turned on a feed somewhere changes stopping it from working. I've had the centre console out and the dash top off so maybe I've knocked something, but what?

Cheers in advance

Liam

[jamienshelly]

Id say you have lost an earth to the speedo, try a temp earth and see if things work if so you have found the fault, its just a case of finding where it is.

[Trevor450]

That definitely sounds like a bad earth. My speedo did exactly the same when the main dash earth on the transmission tunnel was at fault. I had other dash issues so it sounds like yours is isolated to the speedo earth.

[Mr Plow]

Fixed

Bad earth, added a new earth and all is OK.

Thanks all

Liam

[Mr Plow]

Update on the below, all is not quite OK with a new earth fitted.

Lights are fixed, mileage reading is fixed, however the speedo isn't working, the needle doesn't move and the mileage doesn't change.

Any ideas?

Cheers

Liam

[Mr Plow]

Further update, I've checked the wires on the connector, they are showing as follows:

Black - Earth
Green - Ign 12v
Red - perm 12v
red/white - lights on 12v
blue/yellow - goes into the box marked MO559 which I believe is the speed transducer?

Is there an easy way to check the blue/yellow wire?

Not sure where to go from here, I'd like to at least work out if it is a wire, or part at fault.

Any suggestions appreciated.

Cheers

Liam

[Trevor450]

It is unlikely to be the black box - this takes the signal from the tranducer on the diff and converts it to something the speedo understands. I believe it also lets the ECU know what the speed is so it can operate the stepper when you come to a stop. The most likely culprit is the transducer on the diff - they are sensitive to dirt and the correct gap. There are a few topics on this. If it isn't the transducer then it is likely the speedo head itself.

[Mr Plow]

Hi All

Another update. I've changed the speed sensor, still no joy.

When I turn the ignition on the speedo needle moves very slightly, I think this rules out it being the speedo head?

Have I connected something incorrectly if the needle is moving when I turn the ignition on?

I'm at the point where I might need to call in an auto electrician, I rather sort it myself though if I can.

Any other ideas?

Cheers

Liam

[QBee]

I lost both speedo and miles when the thingy above the diff was duff.
It was replaced. All worked.
I lost it again three months later.
Turned out mice had been in the car and had chewed the wires from diff to dash where they passed through the bodywork above the diff.

So anything interrupting the signal from diff to dash will have this effect.

[Mr Plow]

OK, so I've had an auto electrican round this afternoon.

THe speedo sensor is sending a signal through the the box that is sending a signal through the speedo. Its the actual speedo that has had it and needs repairing. I'll be sending this off as soon as I can.

I understand they can take a while to come back, does anyone have a spare one lying around that I could buy or even borrow until mine is fixed? Or know where I could get one from? Its the newer one with an electronic mileage reading.

Cheers

Liam

[Trevor450]

Make sure you take a photo of the milage and let speedy cables know what it is or it may come back with zero on the clock. One of the breakers may have a spare.