Coleton_jl

I have a yamaha 175 enduro DT built in 1978. It is a gem because it has been kept in a garage and runs great. The problem is with the electrical system. It has never worked properly when idle, everything goes dim. at higher RPM's everything works fine. The 'engine start' switch has no function either. is this a typical problem because I have tried almost everything? What is going on?

what is the best website for purchasing parts for my 1978 enduro? I need a break lever and a rear view mirror. Thanks