Mr @ Spotty M,
you can make the various lights go on whlie towing an 747, with no Battery or APU, by using a proper tug (TBL or not) with a running GPU, hook up the pwr cable and switch the bits and bobs on above the capyains seat and there you go, see and be seen
PS, might need the battery on actually to be able to switch pwr to external, can't remember{