Took 2005 FLHTCI for a ride after boosting and charging gauge read over 14 volts but all of a sudden needle dropped to 0 and engine light and battery symbol appeared in gauge. While driving it back home the charge needle would read 8v then 0 and all over the map.
When I shut it off and tried a restart it turned over one revolution then stopped as if I had a dead short. Every time I pressed starter it did the same even after I used a fully charged battery

 

I would first check for loose wires , battery , Starter and all grounds .Mine acted the same and i found a loose main frame ground

Dave

 

If its not a wiring problem then it may be time to check the stator output. The procedure is in the FSN, all over YouTube and in several old threads on the forum.