The easiest way to diagnose a bad igniter is to swap it out with a known good igniter.
If the bike is out of warranty, and a dealer tries to sell you a new $500 igniter, ask the dealer for a "good will claim." Many here have had out of warranty bad igniters paid for in full by Triumph under their "good will claim" program. Odd as it may sound, the customer usually has to ask for the semi-secret "good will claim" program.
