I'm told you can Test (diagnose) the ECU with a test lamp
Can someone point me in the direction of some instructions

(Ive found a few links on here that don't work)

Codes
http://madmagna.atspace.com/tech/diagnosticcodestrts.htm

supporting links/ test equipment
http://www.aussiemagna.com/forums/showthread.php?t=18397
http://www.aussiemagna.com/forums/showthread.php?t=86742
http://www.aussiemagna.com/forums/showthread.php?t=86858


hope this helps