99 Toyota Radio/Cassete/CD combo

I purchased a used 99 Toyota double din Radio/ Cassete and CD player. The unit has two conn's on the rear. A 15 pin (for ext amp) and a 12 pin for which I have no idea.  I installed it into my 94 Toyota Camry XLE to take the place of my single din amplified  Radio/ Cassete player(no CD). I removed the original single din unit and installed the newer double din unit and connected the 15 pin conn. Radio and Cassete player on new unit work fine, CD does not.  It will accept the CD and then searches for a track to play. After about 10 seconds or so it ejects the CD. I've tried several CD's with the same results. I was thinking that maybe the 12 pin conn is probably for an external CD changer and perhaps needed a jumper to make the internal CD function. It seems like the CD player wants to work but can't find a track to play or maybe the CD player is defective. Anyway what is the 12 pin connector for?

I installed this same type unit (no ext amp) standard 2 conn's in my wife's 96 Camry and it works fine.

Thanks in advance