My understanding of electrics is fairly limited (I understand the Smoke Theory, and the water-in-pipes bit makes sense, but advanced fault-finding is usually trial and error. Mostly error. In this situation, my guess is that the switch is making poor contact, and so it will allow the small current required by the engine, but when a bigger load is added to the circuit it gives up. Technically speaking.
This time, work patterns meant that I couldn't sort out a new switch straight away, so I decided to make my own. A look at the wiring diagram, couple of lengths of wire, a few connectors, a fuse carrier, some heat-shrink, and I was in business.
The 'ignition key' was a 20A mini-blade fuse. It worked brilliantly, if I say so myself. The system is robust, foolproof and simple. It has two-point-five drawbacks:
- The 'ignition key' is tiny and easily lost. If you drop it on the floor in the dark, it can take several minutes to find it, even with a torch. Don't ask. And it isn't as easy to find in a jacket pocket as a bunch of keys.
- Switching on and off is fiddly and time-consuming.
- The bike is nickable to anyone with a suitable fuse about their persons.
Anyways, I reckoned that a year wasn't a very good service life for a thing like an ignition switch, so I contacted David to see if there had been a problem with that batch. He replied that he hadn't had any problems with the switches in 20 years of selling them. However, he offered to send me a new one if I sent the old one back with ten pounds. That seemed an exceedingly fair offer, but I was unwilling to take him up on it, as I was only 99% sure it was the switch. He's a very helpful guy, and I don't want to abuse his good nature. I don't rule out an unrelated gotcha which could account for the symptoms. So I bought a new one at full price, and I am going to send the old one back to him for inspection. If he finds it is faulty, I am sure we will come to some arrangement.
New switch fitted, and the XT is going like a good 'un.
But I am keeping the little harness - just in case.