I decided not to drive home in the dark with the Ammeter in circuit, coz the ammeter isn't illuminated, and isn't fused, so if whatever it is were to go wrong I risked blowing F4 and I've no idea what else F4 powers so could end up stuck. So replaced F15 again and drove home. Fuse didn't blow.
Plugged the ammeter in for the drive to work this morning, Before cranking, the current is about 1.2A. After engine start this drops to about 400mA. Opening the glove box adds 1A ish (glove box light comes on). Releasing the hand brake and driving off, quiescent drops to 200mA. Doing things that cause dash lights to come on does cause an increase in current by a few 10's of mA, presumably the bulb currents.
Operating interior lights has NO effect. Operating Seats has no effect. Operating wing mirrors has no effect. Operating windows has no effect. Turing the Climate control Off or to ECO or changing the temperature has no effect. Changing the blower motor setting has no effect. Turning the radio (NCDC2013) on/off has no effect. All of these things still work with F15 removed, so I'm not surprised they don't affect the current readings.
What does affect the current is the accelerator. Hard acceleration causes the current to increase to over 1A. It's transient, so difficult to be precise. Lifting off also causes an increase in current to perhaps 800mA - again transient. This suggests to me that something on the Engine (EGR? SAI? or perhaps the charcoal canister?) and/or Auto gearbox is powered by F15. Also hard steering left or right increases the current too, to the ZF control box probably? However, so far I haven't seen anything exceed 2A total. Or perhaps the fuse that's blowing isn't F15 at all (in which case why do I lose dash instruments and glove box light when it blows)?
The only other newish symptom to report is that he alarm power sounder went off over the weekend. I'd left the fuse blown and been driving about on and off for a couple of days for short trips. When I replaced the fuse and started the car the power sounder went off. I had to turn the car off, get out, lock the doors and unlock again to shut it up. I might try a power-sounder-ectomy.
There is no 'phone AFAIK (would have ripped it out if I knew it was there) - radio is NCDC2013. Only addition I'm aware of is Traffic master (which squawks if you hit the button telling you to renew the subscription). Suspension compressor is unplugged. I'll unplug the relays under the rear seats next.