Can this be left here for a day or so before its moved to the dead zone please?

I've got a mk2 Focus 1600 petrol as my daily. The speedo and tacho have just started over reading massivley. When the ignition goes off the speedo needle comes to rest at 30mph and the tacho at about 2k. Its just started to overheat too and the coolant looks brown (havent seen it in daylight yet) dont know if thatll be related?

Any ideas? Ive tried the old 'dash unlock' and done the gauge sweep etc but the needles just sweep right round and come back to rest where they were
The dash unlock thing showed running voltage at 13.5v too so its not the battery, temp started to come down when i stuck the blowers on full chat so i suspect the fan switch isnt playing ball or something in the dah isnt telling it to switch