ive got the same prob with my 172 cup,only seems to happen when very cold or wet/damp,do you think could be same prob as mine and just replace the batterey?,i also get a strange noise from behind the speedo area,like a crackerling sound???.
Looks like i better get a new battery then,im having a diagnostics check at the weekend to just fod peace of mind as been wanting to do this for ages