i I know this is an old thread, but did you find a fix to your problem? I have an 08 Mastiff and my right front signal sometimes wont flash. Its intermittant as in, the bike is on a lift and one minute it flashes, I switch off then the next it wont.
Check the connections on the back of the blinker. I just fixed mine yesterday on an 04 mastiff with led's. Their terminal connection has 3 wires and to hold them in place they put solder on the tips of the wire to hold them in the block. I noticed they werent touching well to the back of the light. I added extra solder. Heat shrink tubed all three wires together and used some electrical tape to hold them in place to the block. Worked like a charm. They really dont use the best connectors. I like the ones that snap into place. Good luck