2 position pickup selector switch?

I'm new to T-40s; got interested in them and finally bought one off eBay. Advertised as "100% Original and nice low action. Plays perfect. Sounds great." But, while it is in nice enough cosmetic condition, the electronics seem screwy. Mainly, the pickup selector switch seems to be two-way, not three-way. There is only up/down, no center position.
Question: Is this a known configuration for T-40s?
I don't think so; my efforts at getting sound from the bass lead me to believe that this is a modification - one that does not work well. Most importantly, there does not seem to be a position in which both bridge and neck pickups are both in use.
With the pickup selector in the down position, the neck pickup volume and tone controls seem to act correctly. The bridge controls produce no effect.
With the pickup selector in the up position, and the phase switch in the down position, the bridge volume control changes volume, but the bridge tone control also seems to change volume. The neck controls have no effect.
With the pickup selector and the phase switch both in the up position, there is little discernible effect from any of the controls.
So, I'm a bit befuddled now. This does not seem like a good configuration to operate in. I'm working this issue with the seller - perhaps to get a bit of a rebate to cover cost of replacing the pickup selector; but I'm not really sure that that will put the bass back where it needs to be.
Comments? TIA!

Nope, no T's ever came with a two-position pickup switch. It sounds like a previous owner had no use for both pickups at the same time and did a little modifying.

Shoot me your email address in a PM and I'll send you a copy of the wiring diagram so you can wire this back correctly when you get a new switch.

Thanks for your help. I got the new switch installed. I was in a bit of a hurry, but did spot checks of the circuit against the diagram, and it seemed OK. But, after putting it all back together, it still is not correct. The positions play as described before. However, there is now the additional position of "middle" for the pu switch, with the result of now both pickups are in play to some extent with the phase switch down, but only the neck pickup is in play with the phase switch up.
There was a note inside the electronics bay, "Switch overhaul by Brian & Greg 2-18-86" so there was surely some mods done; the pickup switch was confirmed as a two position switch, not some failure of a three position switch. Brian and Greg also scratched their signatures inside the pickguard - Brian's full name appears to be Brian K. Ross, but Greg's was not discernible. There was also an inscription "89-79" with what looked to be initials next to it, but not sure what those were - most likely Brian and Greg's. The serial number of the bass indicates it is a '79 model. Would be nice if Brian or Greg were around to comment!
Anyway, I guess I have to make another try at this when I have more time. If wired correctly, then perhaps there is a bad capacitor, or other component.
I did take pictures of the electronics, so if anyone wants a look, I can send those.
Thanks for your help again!

not exact, but similar sounding problems here
https://peaveyt40.forumotion.com/t339-new-t-40-owner-needs-help

I was sure hoping that all it needed was rewiring to original specs. Have you tried to Google the two names you found inside? Maybe they could shed some light on what type of mod they did and how to reverse it.

I don't know the last name for "Greg", but did google "Brian Ross". Got some interesting results, but nothing I felt I could go forward with.
http://en.wikipedia.org/wiki/Brian_Ross_(singer)
http://en.wikipedia.org/wiki/Blitzkrieg_(band)
http://en.wikipedia.org/wiki/Railroad_Earth
https://www.facebook.com/pages/HiGHER-ORGANiX/22005563655?sk=info
http://www.myspace.com/nosparepartsbluegrass
http://laurenfairweather.bandcamp.com/
That's just a quick scan of Brian Rosses in the music biz, but he's probably now working as a personal injury attorney in Decatur GA
http://www.attorneybrianross.com/
Who knows?
And would the guy remember a mod from over 20 years ago?

It would be interesting to make the contact, but I think I'm gonna just have to gut it out - open the guitar again and do a detailed checkout according to the diagram.

Thanks! I'll post results when that is done.

It was worth a shot. But I would probably do like you said, go ahead and open it up and redo it.

That being said, my main T-60 for several years had been modified. The phase switch didn't do the phase thing, it acted as a kill switch. I kept it that way until I sold it. I did have other T's that were wired properly.