93 Celica stereo questions

Recently bought a 93 Celica GT convertable. The OEM stereo (in the trunk) had been replaced with a Pioneer. The OEM 220W amp is still present under the passenger seat. The only wiring diagrams I've found online don't mention the door (tweater and woofer(?)) speakers or the amp. The problem (aside from a blown speaker in the back) is that only the dash and rear seat speakers work. The door speakers are completely silent. I haven't gone into the dash yet to find out how it's wired. Any suggestions what to look for? As for the OEM CD/cassette unit, aside from 2 of the popout pots not popping out, I don't know what, if anything, is wrong with it. Unfortunately I don't have the anti-theft security code for it. Is it possible to get that somewhere or is it now junk?

In thinking this over (dangerous I know ;^) ) is it possible that the amp isn't working (maybe not being properly powered up by the Pioneer) and therefore only the dash and rear speakers work? What happens when the amp is working? Are all 8 speakers used or just the door ones?