Cleaned the contacts and flipped the spring right way around (I admit my goofs 
) and now I have sound!
Next opportunities for me to get in trouble with electronics:
Wire rear signals as markers to license plate light (currently out), replace heated grips (just in time for warmer weather), and run charging cord to iPhone.
One thing I'm learning is to do one thing at a time, so when things go wrong I have a fighting chance....
