Electrical help - fuel full scale, engine warning symbol on, no tacho

[Scotland North AR]

Hi, not being an electrical type, I could do with a bit of assistance please: -

When I start off from cold after not having used the car for a number of days or weeks, the fuel gauge goes to full scale, the tacho stay on zero, the engine warning symbol comes on on the bottom of the tacho. I drive three miles, fuel goes to proper reading, tacho reads correctly and engine warning light goes off.

Each spring I take the battery earthing bolt out by the battery/ECU clean it up and the other earth wires which go onto the bolt after have that cause me a breakdown on the car at one point i.e. nothing was earthed due to corrosion build up on the bolt and associated earth connections.

As an aside, I have the DRE SLD5 shift lights, I'm sure that the settings are correct but I intermittently get get all the lights coming on at just over 5,000 revs. I've turned the stall indication off (all lights flashing). I'm wondering whether this is an electrical problem associated with the tacho wiring and is associated with the main problem above.

If anyone thinks it's a specific connector somewhere, could you tell me where it might be located please.

Thanks.

PS great blat out in the Scottish sunshine today, a toasty 15 degrees.

[Scotland North AR]

I should have added it's a 2009 Sigma 150 SV.