Whats the best way to clean them?
You'll need to gain access to all of them and disconnect the wires from hand switches,connectors,coils,etc. and clean them all til both mating surfaces are shinier rather than dull;clean all the wiring harness ground connections that contact the bare frame.
I've also found a great product for cleaning electrical contacts/connections especially the ones(solenoids,etc.)that are sealed and are a pain to take apart.
The product is Deoxit and it works.