Licence Plate Switched Live??

I'm looking to fit a terminal block under the seat on the 990 SD so I can power a sat nav, 12v charger, heated grips (if I decide to get some) etc. I have the same thing fitted to my KLV1000, wired through a relay so it switches off when the key is removed, and it works really well. On the KLV there was quite a bit of info on the switched live to the number plate light to tap into for the relay (a grey wire iirc), but I cannot find anything for the SD. The ACC1 is already being used for something else, plus I want to avoid the un-necessary running of a wire from the mask to under the seat when there's a ready made switched live already there.

I've found the multiplug for the light, and it has 4 wires going to it (black, brown, white and purple) thus:



I'm not that savvy with a multimeter. (I hope someone can make sense of this): With the ignition on, I've tried all combinations with the red and black multimeter leads. I get 11.3 when the white has the red lead on it and the black lead is on any other wire. When the white has the black lead and the red is on any other wire I get -11.3. Other combinations produce either 0.05, -0.05, or 0. By my limited knowledge (ironically, my dad was an auto electrician, but he's no longer here thanks to the Big C which is why I know nothing, I always just got him to do it ), I'm assuming the white is the switched live that I can tap into to the relay?

Can someone more knowledgable than me verify if I'm right or totally wrong please?

Thanks,

Andy.

No expert re electrics but have you looked at wiring diagrams in rebuild manual?

Don't quote me but here goes
The brown is ground
the purple is one of the turn signals
the black is the other turn signal
the white is plate light.
this can be tested with ease.