replacing an outside wall mounted light?

Having removed exsisting light, found that the earth and red wires not connected to light. Just two black connected one to neutral and the other live. So I made the same connection to new light, except I connected the earth wire,failed to work. Old light worked prior to disconnection, however checking wires for power source at light none, checked switch, had power. This light switch is looped in to the downstairs ring. In relation to wiring from switch to light this has not been touched, only at point of connection. Could you give me the correct wiring instructions please? Old make unknown, new is a Rydale Pir half wall lantern.

Graham Jones
July 2008