Cause;
- Water leak into tail light unit caused bulb to blow and erosion of socket.

Cleaned socket, replaced globe, checked all fuses under hood & under dash.

May or may not be related to symptoms (before and after changed globe);
- dash lights work only in parker, not full (headlights ok).
- tail lights work only in parker, not full (headlights and brake lights ok).
- alarm has intermitent issues.

A number of related google hits tell me the dash lights and tail lights are connected & the alarm is on the same relay, but i wouldnt know where to start looking for loose wires or ground issues, particularly if the alarm has anything to do with it. All wiring in affected tail light unit appear fine, all fuses healthy and fitted tightly.