Lyric discussion by futatorius 

Cover art for Pachuco Cadaver lyrics by Captain Beefheart and the Magic Band

I think it's about a woman and her car. "Sedan skims along the floorboard" because it's a lowrider. "Her two pipes hummin' carbon cum" - dual exhaust. A Brodie Knob is also sometimes referred to as a Necker's Knob and was attached to the steering wheel to allow one-handed driving. Often amber (or in the case of mine, clear blue) in color. "Spanish fringe..."-- really popular in the 50's and early 60's in lowriders to have a tasselled fringe around the roof liner. Compare the little red velvet balls in Pena. "Looks like an old squaw Indian" like the hood ornament on a Pontiac. "Avocado green 'n alfalfa yellow"-- it's a two-tone car.

The pachucos would really be checkin' out a carrucha like that one. Especially if a woman was driving it.