BHDave, It sounds like it is the same as the greddy egt and oil temp gauges that I have.
Pressing the button on the brain unit puts it into a set mode for setting the peak limit before warning light is activated. When in peak set mode, there should be a red light on (I think).
Make sure you are out of set mode and it should all be good, red light off and button out.
I thought that both my gauges were borked when I bought the car. Both were left in set mode and hidden in the dash. Instruction on the greddy site are for the later version.
I don't have a pic of the control unit and button, but here is a pic of the gauge for comparison.
If you need wiring pinouts, It'll have to wait till the weekend, It is all buried inside my dash and will take a while to uncover.