single wire alternator charfges when it spins at a certain rpm, no light is needed, install a voltmeter gauge to verify its charging.  installing a normal alternator with a light is easy though, wire the pos cable to your battery, of the other two wires one is 12v switched other is field exciter.  run 12v to the light, run the neg side to the field wire on the alt, when light goes out it means the alt is switched on.

thats the problem with a single wire unit, it simply works when it turns but doesnt indicate if its working or not.  maybe a somewhat hidden gauge somewhere in the car to at least to let the owner know the system is charging.  ive seen dash guages mounted on the firewall before, that looks neat