98 cherokee limited, unused connection?

I have a 98 Jeep Cherokee Limited w/ the Infinity sound system upgrade. I pulled the factory head unit to repair the CD player, which was flawless, but left me wondering what the extra, unused connection was in the wire harness. It is a 5 pin connection, but only three pins are used. (A red, blue, and black wire) could it be a CD changer connection? or possibly steering wheel controls? It would be greatly appreciated if could tell me it's purpose. Thanks! Robert F.

I don't know if this makes a differnce but, the head unit is a Chrysler model no. P04704383AE and the Infinity speaker amp is model no. 56007653AC 36670.

its probably for an optional satellite radio tuner.