Gavin, I also am using the mirror motor for trim. A microswitch can be placed so that it will turn on a panel light when the trim is neutral. There might be a problem with space to do this if you have imbedded the motor in the horizontal stabilizer.
I've mounted my motor in the rear of the fuselage with a push-pull cable to the trim tab. The reason is that I put limit switches on the motor, since I found that the force developed could peel the trim tab right off. That would not be good when on short final. Jim Vance va...@claflinwildcats.com