What does maintenanceMode -7 mean on a mongo primary?
Maintenance mode is used when running certain commands, generally the compact command.  What you have here is the bug mentioned in SERVER-9338 whereby I am guessing you have run the compact command against your nodes several times.  There are some circumstances, especially when run on a primary when it will usually cause a change of state (i.e. it's not primary when the compact finishes), that cause maintenanceMode to be erroneously decremented.

As of writing this answer this is fixed in the development branch and has been marked for backport, though it has not (yet) been targeted for a release in the earlier versions.  Until the fix is released it should be safe to ignore the value, but I will do some testing to confirm and report back.