Turns out it is the connector or switch itself - I did try adjusting it first time, done it again and found that if I press on it in a certain position, it works, but only just. I'll have to take that to bits now, find out if it's the connector or switch. No biggie though. The connector is tucked under the master cylinder, nowhere near the banjo bolt! So I won't have knocked it when fitting the lines. Only thing that I can think of is that when you fill the brake lines, you're taking the brake lever all the way back to the handlebars when the bleed nipple is open, and you're doing that a lot, so that could have knackered the switch itself. In the meantime, I think if I put a rubber band in there to hold it in position, there's no problem.