Just mounted one on my 185 sport, I just ran the two wires back to the fuse block underneath the dash. If you don't have that option you should have power to the front light, you will just have to have the light switch on to power the unit. Don't use the trolling motor batteries as you will get interference.
I powered my bow mounted 240 from the bow flip light. I never cared for the light so I disconnected it and used the power supply for the Garmin. Has worked out well for me.
I have recently mounted a finder on the front of my Pro Angler. I spliced into the lights, but I had three wires, one ground, one hot when the light switch is on, and the other is constant hot. I spliced into the constant hot.