960 electrical problem

[jonemory]

i have to leave my key in the on position on my car for several minutes before i can start it... my temperature gauge will go crazy and my check engine light will flash and sound like a machine gun... my car always will start but after several minutes while the temperature gauge settles at the temperature it is suppose to be at... also my engine fan will come on even when my car is cold.... it will not start until the gauge settles back at where it needs to be... i used to have the problem with my code reading for the temperature sensor i have replaced it three times and it never changed the problem... is the problem in my ECU or is it something else possibly a wire or a faulty gauge... thanks