Call Power Acoustik and tell them you had it for a few years and used it in a few cars so the harness has been chopped so short you need to get a new one. I'm sure if it was originally yours, they will want a receipt for the stereo brand new and they may sell it to you if it is available. If not, I sell new Soundstream Stereos at a very low discounted rate, as well, Power Acoustik.
Check out the link below, we are the lowest price online for any of their products because we are closing all of the products out since they have driven the product line down to portray them as low as Dual and Craig., as a matter of fact, the products are all great, but, they do not protect their dealers and allow distributors to sell them online on Ebay, cheaper than the delaer's cost with free shipping, which has driven us away from them because we can't make a profit.
Anyway, they should be able to sell you one, if not, give me a call or check our site, we sell their distributed products as well and may have a harness available on the website.