If that's the commercial I'm thinking of (not sure at all) the song is Bang a Gong by T-Rex, a rather obscure Birtish group from the early 70's. Actually not sure which song it is, just remember being amazed to hear T-Rex on the idiot box. Course, if Led Zep is so broke that they have to sell their songs to Cadillac, well...
I may have the commercial wrong, because the song I'm talking about is very hard and fast, not trancy at all.