What the hell is all this talk of wiring? Am I missing something? Every single time I've ever done new gauges/overlays all I do is pull the needles, lay the gauges on, put the needles back on and go. Obviously record where everything was first and get everything accurate. Put the needles back on with power to the cluster and make sure you take a picture beforehand so you know exactly where to go. Start the car for the tach and place it right where your sweet spot is at warmed up idle. For the speedo, I drive around with a GPS and the cluster cover off and play with it till I get it right.
edit: If these glow gauges do require some other source of lighting like if there is a wire coming off them for ground/power. Just tap into your ground/power... find a wiring diagram and splice away. Not rocket science.
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.