I've just finished re-wiring an old Land Rover and found exactly the same problem. The clip-on labels are no use, unless you constrain them either side with heatshrink (otherwise they just slide axially into oblivion). Laser-print under transparent heatshrink sometimes works, usually doesn't. In the end I used an ordinary Brother hand-held tape printer set for small print, with the tape making roughly a 'P' shape around the cable; the cable in the circle of the 'P' with the print on the tab formed by the limb of the 'P'. The end result looks a lot like that in AndyF's linky. It's oil-proof, waterproof and cheap.