clio 1.4 electrical gremlins

Hi really hope someone can help me and my son.

We have a Clio 02 plate which has done 71k it's a 1.4 16v Dynamique. Here's the list of issues, we have experienced.

1. The rev counter revs for a few secs and then dies!
2. The temp gauge warms up and then dies!
3. The immobiliser lite comes on when engine is running, when it does the indicators and elec windows refuse to work, but the engine still runs.

What have I tried so far:-

1. Checked the relays all work.
2. I have checked all fuses and cleaned out the fuse box.
3. Wiggle checked connectors.
4. Battery negative tried another earth from battery to engine lifting eye.
5. Cleaned the speed sensor.
6. Cleaned the temp sensor.
7. Oh today found what I thought was a broken earth wire, for ref it is the one at the front of the gearbox LHS.

We look forward to suggestions and guidance as to what we can do.

Thanks

Matt