The fuel sender units normally just need a clean up. You test them with a multimeter ..if you havent got one, they are a basic electrical test instrument .A cheap one will be OK for automotive use.
You place the multimeter leads on the wire resistor inside the sender and move the arm up and down and watch the resistance on the meter. Usually, you want it from around 1 to 50 ohms but it varies with different senders.
read this
http://www.ladyada.net/learn/multimeter/
The toggle switches look nice !
Mike