Good evening ape,
Thanks for your appreciation of my XB-120, by the description of your pots and switch, I could say that your XB-400 is surely an introductory year (1994) model. It probably share the same electronics and wiring pathway as for the predecessor Mercury Series MB-4 and I think that psp742 got the same bass as your. He just post not the Washburn Club thread of TB and told me that he will post the picture of his bass internal bay as soon as he gonna fix a problem with Photobucket. He didn't write if he will post on basschat.co.uk or on TalkBass (TB). I keep you in touch if your not also on TB.