Shallow men believe in luck.
Strong men believe in cause and effect.
Ralph Waldo Emerson

For purposes of our discussion, let's distinguish diagnostics from troubleshooting. We will assume that diagnosis involves analysis of externally-available information, and troubleshooting may involve physical contact and disassembly. It is possible that someone gathering diagnostic information might come in contact with an equipment item to observe externally visible conditions, but that contact is not the same as troubleshooting.

Further to the horn example from the last chapter, horns frequently grow legs and walk away (are stolen). As a result, when the horn doesn't work, it is a good idea to start by determining if the horn is still there. If not, you will know the failure mode - "Horn - Missing". If the horn is still there, it would be useful if the operator can check to see if the air system is functioning at normal pressure and that the electrical system has power. Again, these checks do not constitute troubleshooting; they provide additional information to help form the diagnosis. If the tubing that provides air, either to the solenoid valve or to the horn is in plain sight, it would be useful for operator to look them over to see if they are crushed or broken. If the wire to the solenoid is exposed, it would be helpful if the operator can see if it is cut or grounded. If this kind of information is unavailable, it will be necessary for the troubleshooter to...