i always test mine out with the cig lighter harness
take that portion of the center console off and unplug the harness that goes into the cig part...
then slip the wire into the harness in the right spot...ground and power
these gauges are always lit don't forget and take pics
if your's are the same setup, there should be a purple wire..this wire can either be connected to an illumination wire that has dimming enabled on it and allows the gauge to dim when you dim everything else.
otherwise, you connect that wire to a ground for full brightness at all times, this is what i did.