2nd gen Colt stereo wiring

[zsn0w]

I've got a 1974 colt I've been working on getting back to complete running form before swapping in a 4g63t, and I have a stock stereo I've swapped into it (it was a factory stereo delete car). Because of this, there is no speaker. The speaker output, from what I can tell, is a three prong 6.3mm plug. The only other output on the back of the stereo is a two prong plug that has a plug on the back of the gauge cluster seems to be supposed to plug into (it's right there and there's no other socket for it?). So, this is kind of a longshot, but does anyone know if: a. the two prong plug on the gauge cluster is supposed to be going to the back of the stereo, and b. the three prong plug does go to the speaker? I don't have a factory speaker to mess around with to figure it out. Finally, if both of these are correct, what are the three outputs of those prongs to the speaker? It only goes to one speaker, so what could the third prong be?? Thanks.