I'm having a few problems with my 406 and need some help to point me in the right direction

Right, 1998 2.1 td Estate.
1st fault -My air-con wont kick in, its all gassed up and if i manually trigger the clutch the AC will work. Are there any common places for broken wires etc? or is there a ecu failure ?
2nd fault - The fuel gauge is up and down the a prostitute's knickers ! Again anything common ?
Thanks in advance

Ian