How about this:

CREATE TABLE [#cars](

[id] [int] NOT NULL,

[part1] [int] NULL,

[part2] [int] NULL,

[part3] [int] NULL

) ON [PRIMARY]

INSERT [#cars] (id, [part1], [part2],[part3])

VALUES(1,1,1,1),(2,0,0,0),(3,0,1,0),(4,1,0,0),(5,0,0,1)

SELECT * FROM #cars

SELECT id, part1 as Part, 1 as Seq

FROM #cars

WHERE part1 <>0

UNION ALL

SELECT id, part2 as Part, 2 as Seq

FROM #cars

WHERE part2 <>0

UNION ALL

SELECT id, part3 as Part, 3 as Seq

FROM #cars

WHERE part3 <>0

DROP TABLE #cars