Well you were all correct. Charged battery for several hours whilst refitting turbo and swapping glow plugs and controller, and when reinstalled, all electrics seem ok.
Have a few Undervoltage shadow errors that scanner1.4.0 won't clear, but they flagged yellow, ie not present so I'm a very happy chappy, well, as happy as can be as car still low on power (well, worse actually, but I'll add that to the turbo thread).
I did clamp both cables together for a good while, and used the little pull release for the boot (really wish I'd known about that last night!), so thanks for the help folks.
I'll leave the side conversation of drag for another day

)
Thanks everyone, panic over lol
2005 (55 plate) x5 3.0d sport, auto trans, nav tv thingy, but no dsp.
Under a turbo swap presently (fingers crossed it fixes her!)