Is it okay to hook up an additional 112 speaker directly to my 110 speaker combo amp? Will it damage the amplifier by adding an additional speaker? It's not wired for another output, no external speaker, but I'd like to install one.
Just literally wiring in an additional speaker in addition to (or even in place of) the existing speaker is likely to result in damage to the amp and/or speakers. A key consideration in this is the idea of impedance matching -- the amplifier electronics, the power amp in particular, are designed to operate against an electrical load with specific characteristics (impedance).
There will need to be additional modifications to the amp, wiring or speakers necessary to add an additional speaker to a combo that is not already designed for it.