120 line to 5v signal

[skimask]

Can't you butt a lever switch up against the valve itself? Valve arm hits the lever switch, connects the dots, send the 5v...
Or do you need an actual voltage that is proportional to the voltage going to the valve itself?

[AMay]

No, a small motor turns a shaft using gears. The limit switches are operated by cams on the shaft. There is not room to add another microswitch,

[skimask]

No, a small motor turns a shaft using gears. The limit switches are operated by cams on the shaft. There is not room to add another microswitch,

120VAC when the motor is at the limit? Maybe tap that 120VAC, plug it into a small wall-wart like power supply and send that output to the controller?
Past that, I would think a series current limiting resistor along with a voltage divider (and maybe a ZENER for protection) would do the trick...or a voltage divider that divides it down to +12v (or whatever) and feed that into a 7805 regulator.

I do like your light bulb idea though...simple, effective, practically zero thought/effort required
Did something like that awhile back. Needed to switch 120VAC with a PIC. Didn't want to mess with the AC, so I took a PIC, a servo, a chunk of threaded rod and a standard wall light switch...programmed the PIC to move the servo to move the light switch handle to turn power on/off. Almost perfect isolation...