It's pretty simple. First you need to find an ignition power source to turn it on. I ended up using the radio igniton wire which was red. To power the little light bulb, I tapped into my dimmer lights so they work with the headlights and dim. Ground the gauge and the backlight. and the sender wire goes on the sender which replaces the factory sender to the right of the distributor. In mine I used a T- fitting so I could keep the factory, and the Autometer one at the same time.
On the pic of the back of my gauge, YELLOW is my sender wire, GREEN is igniton power, WHITE is power for the backlight, and BLACK AND BROWN are ground.
Hope this helps...
Others will tell you what I missed