my tail light on my speedfight 100 not working when i put my lights on but when i put on the brake it lights up i have replaced the bulb with a new twin filement bulb and it is still not working all other electrics are working fine.
I have the Workshop Manual for that bike, It includes loads of fault finding help, Pictures, Part lists & wiring diagrams etc. If you would like a copy email me @ slippery.steve@ntlworld.com
Or look at my small guide I posted @ http://www.howtomendit.com/answers.php?id=143363