You report: " I have no light or battery trouble!"

• a destroyed (burned - you even can smell it) regulator (by short circuit or polarity error)
• missing or damaged wires within the old harness
• damaged battery (internal shortcircuit, bad electrolyt - even in new batteries!)
• corroded switches and/or lamp sockets / bulb holders
• shortcircuit inside electric horn (very often!)
• all is OK, but you get far too low Voltage values (especially digital ones)