mpt

Any ideas with this,
What is the single pink wire for? It is on the back of the doulbe din head unit,no conections just goes into the back, is it something to do with permanant power?

I have replaced the doulbe with single size unit now, it all works ok, but noticed today that when the ignition is turned off then back on the CD(mulit) starts from disc 1, when it was playing from disc 4 for example before the power was switch of.The head unit's memory works ok for radio names/disc title etc, is this something to do with the pink wire?
If so were should this wire be conected to?

Thanks.