1990 Ford Probe relay question

[caddyman379]

Hey,

All my interior lights are non-functioning, (except the dash lights,) the electric headlamps do not raise (however they do light,) and when i was looking through the Fuse/relay block next to the battery, I noticed that the Main 20A fuse or circuit breaker was missing, could this be causing any of the problems im having?

Also, Im looking to put in a stock radio, are there any guidelines I'd need to follow to do such?

Thanks for your help!