you're gonna need to find a wiring diagram for the ignition stuff..idk which wire that is.
thats why i used the radio...i already had a deck in and i knew which one was power/ground.....its usually pretty simple though as red is power and black is ground 99.9% of the time. if you wire it to the radio...u just have to turn the radio on for the gauge to be on...but mine was always on.
for how you connect the wires....if you want a no worry good install you should solder and use heat shrink .
if you;re lazy like me and you want to install it in 5 minutes you use wire nuts