When you connect up to the hold switch you just need to check with a testmeter which of the two points are needed. There appears to be a changeover switch here. (Three connections) but be aware as the format seems a bit unconventional.

Snip off the broken piece of ribbon cable and solder wires to the correct points. This neeeds to be shorted or closed for "lock" and open for unlock. Check this with a meter before connnecting.

All that remains now is to carefully tuck the wires into place and replace the top of the Nano. Since bare wire strands were used, It needed a squirt with the wife's hair lacquer - after masking the ipod off, of course!

This may sound a bit long winded but don't worry. There's usually plenty of ribbon cable to practise on. I didn't get it right the first time. Especially with the sandpapering. The procedure is also very forgiving insofar that you can keep trying with the same bits.