E30 Zone

Hi all, I need your brains.

I've swapped the instrument panel in my 1990 320i Cab with one from a car that was scrapped. The seller was sure that all the gauges were working in the donor car, but the fuel gauge is reading empty, even though I've got half a tank. All the other dials work fine.

This is my everyday car, so I can't be driving around playing russian roulette with the fuel-tank!

Some info you might need to know:
The panel I took out had a sky blue back panel, whereas the replacement was white. The panel I took out had a little white chip with BMW13 then a serial number at the bottom right below the dials, and the replacement one reads BMW01. I tried swapping these over, but the rev counter and mpg started wiggling even without a key in the ignition, so I dunno if that's related.

There's nothing wrong with your new fuel gauge - it's just the wrong fuel gauge.
You have fitted one from a car with a smaller 55 litre fuel tank.
If you fill your tank completely, you'll find that your new gauge will read full, but it will fall twice as fast as it should, and read empty at half a tank.
Low fuel light will still work properly.
Twitching rev. counter sounds like one of the odd characteristic minor faults that occur with instrument clusters fitted with SI boards fitted with lithium batteries.
Why did you change the cluster?

I went over a bump hard, and ever since then my speedo was dropping out intermittently. When I tapped the speedo it would respond so I know it's loose behind the dial (as opposed to on the diff). I'm gonna try and solder any loose connections on my original speedo, but I wanted a backup in there just in case.

So the white box thing under the temp gauge, is that the SI board?

SI board is the complete electronics package for the instruments, apart from the speedo. It stays in the front half of the casing when you split the cluster open.
For the speedo fault, check the soldering to the pins where the speedo daughter board plugs into the main board.

OK, thanks.

What IS that white cartridge thing under the temp gauge? It looks like it's designed to be removed easily, and it's got what looks like a serial number under it.

It's the coding plug for the rev counter. Tells it whether to read for a four cylinder pulse input or a six. Use your original.