Hey Bill,
I went by the Best Buy on South Fwy and couldn't find the an FM modulator like you described. The closest thing they had was one for a Sirius radio. It was from a company called Directed Connections. But it required a signal from the Sirius radio to tune the FM modulator. The little sales guy was no help. He couldn't understand how I could have a car stereo that didn't have an auxiliary input on the front. I think I have tires older than him. Can you further identify the one you bought?
Thanks,
Leon