The Interphone spotlights arrived today and I have to say I'm very impressed. They appear really well made and finished, and are surprisingly heavy: The wiring that comes with them looks like it should enable an easy fit if you want to use their separate additional handlebar switch, but I of course want to use the standard switch and dash warning symbol. So I'll be bastardising the Interphone loom. Interestingly the Interphone loom has a MOSFET wired in under some heatshrink to act as a relay which cuts the power when the ignition is turned off. I think I'm going to try and use this instead of the Fuel Pump Relay I was going to use, as it should do the same thing but is smaller. The lengths of wire are all wrong but I can sort that easily: Unfortunately I'm now fully committed to other life stuff until next weekend, but I'll have it fully planned in my head by then.
I went to bed last night after making the post above and the wiring diagram kept me awake as it shows the full current for the lights going through the small handlebar switch. It's less than 2A, but still it didn't feel right to me. As soon as I got a chance today I made 10mins to whip the Heatshrink off the MOSFET and see what's going on. The result is that the wiring diagram in the box with the lights is complete B0ll0cks: What's actually happening is the main power feed doesn't go anywhere near the handlebar switch and it's the switch feed to the MOSFET that the switch is controling. Like: I think I'm going to revert to Plan A and use a Fuel pump relay to switch the spotlights.
But the MOSFET's Gate current will be small, so why can't you use it as you intended (as per your updated wiring) as the MOSFET is just an electronic 'relay'?
Yep, been thinking about this whilst spending too much time driving up and down the country. I can use the MOSFET by simply connecting the signal from the Ducati loom direct to the Gate. It will need the Interphone loom to be shortened significantly to be tidy, but I'm quite good with a Soldering Iron.
Finally finished this off today. On the Left is everything I cut out of the Interphone harness, and after adding the mating connector I ended up with what's on the Right. Note the MOSFET is under the heatshrink: Excuse the state of the bike, it really needs a clean: And with the warning lamp showing on the dash:
