2006 M45 Sport

I have this loose wire in the engine bay, it is on the driver side of the engine block.
Any idea where it should be connected to ? The car occasionally fails to start. A mechanic checked starter, starter relay, ignition switch, fuses, battery, battery wires and connections for corrosion.
No faulty parts detected. The battery made in March 2021, full charge.

The next day after the car had been under a heavy rain it fails to start: all instruments turn on, two loud clicks and the engine not even trying to turn over.
Most recently would not start for 3 days and then miraculously started with nothing done to it.
Any ideas ?

Thank you.

I don't know specifically on an M45, but that type of braid is generally used as an auxiliary strap between the block and chassis to assure a good block ground. Sometimes it's also used to ground portions of the exhaust system that may lose ground contact because of a rusty manifold or manifold studs.

Your starting problem sounds like either bad starter brushes or a bad ring contact in the starter solenoid. The loud click you're hearing is most likely the contactor ring in the solenoid pulling in, but for whatever reason the juice isn't reaching the starter armature. Usually the cause is worn out brushes, but in any case it sounds like you need a new starter.

Thank you !