I'm not sure that I agree totally with that, but the electronics do play a large part in shaping the final sound. I also beleive the wood, or not-wood (eg aluminium or graphite necks) as well as the neck connection method (BO, NT, set) play a part in the tone too, more than 10% anyway. But all of this can be highly contentious.
For construction advice, spend some time searching and reading through the link below. Lots of useful info from luthiers, rather than just an electronics type like me.
http://www.talkbass.com/forum/f57/
I'd also spend some time reading through the FAQ section in this sub-forum, especially the Dimento's threads, as luknfur did all of his pickup experiments with two basses with big bathtub routs and the same types of strings.
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