Thanks, Texmo. I'd guessed that this might still be the problem, but never having worked on one of these before (it's my first "Yank" truck although I've had Harleys for years) I wondered if it might be a quirk in the switch or suchlike.
Strange thing, though, is that it was the right-hand side which I fixed to sort out the other problem. I'll try doing the same for the left side, see if that helps.
