S40 (New) Electrics : S40 boot light doesn't work

[Acuity30]

Really confused by this. I went to replace the halogen festoon in the boot, and swapped it for LED, but it doesn't light up. I checked the old festoon and it hadn't even popped. I've tried multiple bulbs now and still nothing so I put my multimeter on the bulb holder terminals and it's not getting any voltage.
AFAIK the same fuse that powers it also powers the fuel level gauge which is working fine, so can't be that. I can't check voltage at the plug (i.e. before the bulb cradle) as the holes in the plug are too small to get my prongs in.

I don't believe this is related to the common boot loom failure because:
The reg plate lights work fine
The 'boot open' warning works fine, is only displayed when the boot is open
The rear lights all work fine
The button on the key to open the boot and the manual boot release button both work fine also

How can I access the main wire for the boot light? It goes up in the fixed parcel shelf and I can't see where it goes after that. I tried removing the top felt/foam off the parcel shelf for a better look but couldn't figure out how to do that either.