No temperature gauge operation on '99 Tracer

[formzy]

Hello,

A friend has this car and has little or inaccurate temp. readings on the gauge. She has two sensors,or one sensor (coolant temp. sensor) and one switch(coolant temperature switch) next to one another. I think I bought the wrong one-coolant temp. sensor. I was told usually the coolant temp. switch is the part at fault with no or inaccurate gauge operation. Just wondering if anybody has come across one like this on their Tracer?
I believe she has the basic 2.0L engine, but is it a different part on the dohc 2.0L Zetec engine? Any ideas or tips appreciated.