I've got a Garmin Echomap 93sv that I plan to mount on the bow of a 2006 Tracker 190tx. I don't see a power wire for electronics up by the bow. Can I attach it to the wire that goes to the tilt/trim switch at the bow?

Your best bet for wiring modern electronics is to run dedicated wires from the unit directly to the engine cranking battery.  I’d use 10 gauge wire with the factory fuses that came with the unit. 

I agree running  separate wires would be the best. I couldn't on my boat so I feed the bow fish finder to the bow lights. No problem so far.

Running new wire to the battery is no doubt the best solution. However, from briefly looking under the bow plate and reading comments from other people running wire on Trackers, it's a pretty big job. So, it may depend on how much work that is. If anybody has suggestions on running wire in a 2006-era Tracker, I'm all ears.

I ran mine back to the console to the buss I think that is what it is called.