1983 Honda Prelude Car won't start with key

Electrical problem
1983 Honda Prelude 4 cyl Two Wheel Drive Manual 100k+ miles

my buddies honda we're fixing wont start when we use the key in the ignition, we can cross over the starter to start it and the starters new. I was told that it could be the ignition relay, clutch relay, or the ignition switch. My major problem is we don't know witch one it is or how to find out witch one it is