The dome light in my Impreza has a three way switch that in the full rear position remains off even with the doors open. In the middle position it is on auto so that when a door is opened it comes on. And in the full forward position it stays on constantly. If yours has a switch you might try moving it to the middle position or the full rear position per your preference.
Test gauge function with a mechanical gauge to get actual engine temp.
The temp sending unit or gauge is bad, probably the sending unit.
Because the gauge is broken.
You have a problem with the engine controls, have the codes read at the dealer or an auto parts store and make the necessary repairs and the light will go out, or it can be reset by the tech.
Most likely cause is a failed engine thermostat.
With no make/model/year/engine information to work with...The temperature gauge is driven by a simple sensor that is both cheap and easy to replace.Any auto parts store will be able to help you find it on your engine, and of course more than happy to sell you one.
Thermostat is sticking.
The thermostat is the most likely culprit. The major clue is that the engine temp stays in the lower middle of the gauge - the heater core would not cause this. The thermostat is most likely stuck in the open position - needs replacement.
The gauge, wiring or sending unit is bad.
probly bad gauge or loose wire buy a manual gauge one with the oil line right to the gauge nothing is wrong. the guage is supposed to be high when driving. it will drop when you stop or are idling.
i have a 1990 ford ranger and my fule gauge always reads full, why?