Very old appliances may have different colours in the flex. Examples of these are shown here.
Plugs of this age will not have insulated pins, so the plug should be replaced with a new one.
The Black wire connects to the terminal marked N or Neutral.
The Red wire connects to the terminal marked L or Live
The Green wire connects to the terminal marked E or Earth.
Older appliances are likely to be Class I (with an earth wire), however if they are Class II, there is no connection to the Earth terminal.
While old appliances can still be serviceable, it is likely that the flex will need to be replaced after 40+ years, particularly if it is rubber insulated.
Very old appliances may not meet modern safety standards, and therefore should be thoroughly inspected and tested before use. This will normally involve partial or full dismantling, to ensure the internal components are still in good condition.