My hour meter reads a minus 86.7   I someone posted that the polatity was hooked-up backward.  This is very unlikely in my case.  The hour meter has never been unhooked and ran fine from the beginning.  I have changed the battery but I now the difference between + and - and Red and Black.  As I understand it, the hour meter monitors the time between oil changes.  If true, how does it know.  Also, I have just changed the oil and filter and it did not re-set the meter.  Someone please give me some schooling on this issue.