I'm not in the US, but my car didn't have an ISO plug.
I had to get a Ford to ISO convertor (About 15 UKP, including the speaker connectors)
However, as I have 2 head units, I've spliced another ISO (with just the power wires) into the convertor (Actually, it was spliced for the Mk1, I just found another ISO plug and stuck it on the wires for the Mk2... When I say spliced, I mean all nicely soldered and heatshrunk... =)
So see if you can get a convertor before chopping the wires off.
Jazz
(List 112, Mk2 12 gig #40. Mk1 for sale 4 gig #30, apply within)
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Jazz
(List 112, Mk2 42 gig #40. Mk1 4 gig #30. Mk3 1.6 16v)