Speaker wiring harness issues

[cubsox]

I'm trying to replace the 6x9 speakers in the rear deck. I've got the new speakers installed, but I can't hook them up to the factory wiring harness. I ordered the new speakers from Crutchfield, who sent an adapter that was supposed to fit. The adapter they sent was a 2-pronger, but the factory harness is a 4-pronger. I contacted Crutchfield and they said they did not have any harnesses that would fit. I've looked all over the internet for 4-prong harnesses that will fit, but have found nothing but 2-prongers. Does anyone know where to get a harness that fits, or do I have to make a modification with the stock harness from the old speakers and the spare wires from the new speakers? Thanks!