Anyone on here know of some good forum sites like this one for bigger over the road trucks. My dad's water temperature gauge is acting up on his CAT engine and need to eliminate wether it's the sensor or needle on gauge.He says it fluctuates, and triggers the overheat light on. anybody have any thoughts?

3406 is way too broad.........What model a/b/c and what year or type of truck or piece of equipment is it in. They have been around for many many years.

It's on a 99 Peterbilt. Engine is a Cat 3406 E-model. 550

Get an infrared temp gun and see what the temp is where the sender is. Sounds like a bad senor or bad wire or connection.