Ok had exactly this issue and it does appear that Dyson engineered the solution to prevent high current drain with stuck motors. Took mine apart and occasionally got some power to the brush head but normally no power at all. Maybe a dry joint on the PCB? I have no idea. So I did a brutal hack. Turns out the +ve power is connected from the battery input to the power tap off whatever happens - but ground is switched. From the photo, ground/-ve is the white wire. Handily right next to the feed from the battery. I dropped a big blob of solder across the wires, so now the accessories get the full blast from the battery when you press the trigger. I really don’t recommend this fix, but it was (to me) preferable to giving Mr Dyson a few more £’s for his poorly made devices. The V6 now powers the accessories “like new” and I’m not surprised. I think the motors are rated at 18v and now they are getting the full 22v juice from the battery pack!