Speedometer intermittent failure

[TomHylso]

Hello. I have a 2011 Impreza and lately the speedometer only works when it wants. After looking around the net and doing some troubleshooting it's down to the cluster or an earth fault cause the cruise control works and if i quickly turn the head lights on/off it comes back to life, kinda like shocking the system voltage or something. I do not want to replace the cluster if it can be fixed in any other way. It states the cluster can not be serviced but is that true ? Cause i think there is just a loose soldering point in there somewhere. Could the fault be outside the cluster ? Considering the cruise control works it's not the sending unit i presume they both use the same sensor. So any advise would be welcome and if anyone has taken one of these apart and done a repair let me know.