Handbook 652 Body Electrical Diagnosis Glossary of Terms If you are looking at a system circuit and find a component you cannot identify, refer to the Glossary of Terms and Symbols. and Symbols In the illustration, note the two types of Manual Switch – normally open and normally closed. The state of the switch refers to its “ at rest ” state in the circuit. Looking at the three different kinds of Relay in the illustration (normally open, normally closed, and double throw), note they are shown with the relay coil not powered. Technical Training 57