Is there anyway to power up a head unit without installing it?

if the head unit im thinking of is a in dash cd player then yes. on my old stereo i just had to hook up the negative to the negative side of the battery and the red one to the positive side. on my new i have to hook up the yellow and the red together and touch the positive. be careful and make sure you hook it up to right sides, it will blow up the deck if done wrong. good luck

You may want to hook up a speaker to the individual speaker leads as well. I've seen someone buy a used stereo that powered on fine, but the internal amp was shot, so he got no audio... Just my .02

you can hook the wires together to a cig lighter plug, works all the time.

or use your battery. put the power wires on it, and ground the black. should come on if it works.