Because of the age of your engine I thought it had the newer t/t wiring with relays. I don't see any relays inside the cowl leading me to believe you have a three wire motor.These motors used about 10 gauge wiring and none was inside the engine.Red wire attached to battery positive and the center of the switch at the dash. Black from the motor attached to the battery negative, Green and blue are connected with an automotive type quick-connect. If you want to wire in a switch on the engine you will need to modify the system to use relays--it is very simple-- or if your switch is capable of carrying 30 amps, run some red, green and blue 10 gauge wire out the cowl and splice into power, and the up and down wires. Red will pick up power from the battery side of the solenoid.
Again, this is not difficult BUT it does have the drawback that every time you use the trim you are moving around a LOT of current.
I have changed a three wire motor to relay system and been very successful. The only thing needed to be done out of the ordinary is to either insulate the relay power ground--not signal ground (since the motor is already grounded.) OR clip off the ground prong (I think it is the center one) of the relay..) I prefer insulating so that if you ever change to a two wire motor, the relays will still be good.
I did this a couple of years ago and there is a post showing the wiring. RRitt also added to this thread. So, you should be able to search it. ----Right now it is too much trouble for me to search out my photos from the thousands I have on my flash drives and repost them