Morris Minor Owners Club

1968 1000 Traveller. I have just replaced a blown instrument light bulb. On replacing the speedo in the panel, the fuel gauge reads empty (with a full tank). If I remove the speedo again, the gauge reads normally and in addition, the instrument lights come on despite the light switch being in the off position. Anyone have any thoughts please?

It sounds like the gauge terminals are hitting something as the speedo is positioned, push any nearby wires away from where the back of the speedo sits. Check for loose wires or broken insulation. Sorry it’s a guessing game, not being there !

Crystal Ball time, with a fair bit of logical thought process..

On refitting the Speedo, you've clearly disturbing, i.e., breaking a connection at the Voltage Stabiliser, that's why the Fuel Gauge isn't working.
However, Instrument Lights coming on, well that connection to the Voltage Stabiliser is apparently shorting to the Instrument Lights.

So you'll just have to conduct a thorough examination of all the wiring and connections in that area; you'll find something eventually.

Only you know the condition of your car's wiring, the older and dilapidated it is, the greater the chance of these things happening.
Assuming it's the original loom, it's 57 years old, long beyond it's intended lifespan.

I have checked for anything which may be contacting the back of the gauge and giving a spurious earth. My understanding is that the speedo needs to get it's earth from contact with the dash when it is pushed into place, but everything works as it should when the speedo is out of the dash, so it must be getting an earth some other way?

Do any of your speedo lamps ( turn,ignition , oil ,battery etc. ) have fittings with earth attached?

John ;-)

The oil pressure lamp sender earths through the engine block.
All the lamps including the two speedo illumination lamps work with the speedo out of the dash.

Speedo drive inner?

John ;-)