Replacing Aftermarket Stereo

I was hoping maybe someone here could answer this for me:

I would like to replace the aftermarket deck in my truck that was installed by a stereo shop and I was wondering if I can simply just plug in whatever harness they put in there to a new deck, or will I have to wire up a new harness specific to the new deck?? Appreciate any info..........

More then likely you will have to wire in the new harness unless the new radio is from the same manufacturer and a similar model/year.