Ignition on power in a 65 dart

lights for my aftermarket gauges
I'd see if there is a connector in the instrument light circuit already for an option console tach. I don't know if '65 had that option.
Look at your fusebox, but IIRC that circuit (with the dimmer control) both ends of the fuse are crimped connections. if not you can use a piggyback. May need to add a 2 amp fuse.
upload_2019-8-5_9-28-24-png-png-png.png
aftermarket gauges
Those probably require 12-14 Volt power source.
Chrysler used the middle fuse position for tach, but on your car's fusebox that may be alrady taken with a higher current fuse for the 'vert????? Or maybe not. My '67 is a hard top, so I was able to use the factory solution for my aftermarket tach and under dash gages. Pictures here in post 8
Use the factory fuse ???
aftermarket horn
Horn wasn't fused. Not sure how yours gets the power but probably in the engine bay. They seemed to move th ejunction around every year. Shop manual will show it.