Engine temp gauge not working

[Tuma]

2000 Pro Air - Gt 40 What should I look for to troubleshoot?

[TRDon]

Make sure the gauge is getting power first. After that is proven good, suspect the sender. Senders are pretty cheap and typically waht goes out. You might want to try grounding the wire to the engine (the one from the sender) and I believe that will make the gauge go full sweep, proving the gauge functional too.