For other wiring I find that PVC insulated hook-up wire of 7 strands of 0.2mm dia. Conductor, usually termed 7/0.2, is okay up to 2 Amps while 10/0.1 is good for low-current lighting circuits. If you need very thin cable then I suggest buying multi-core alarm cable which contains 4, 6 or 8 different coloured insulated multi-stranded cables inside one outer sheath. Others have used telephone wire or enamelled copper wire, but you have to scrape off the enamel insulation on the latter type in order to make a decent joint.