I do not think "THE" harness problem is your problem. The starter circuit doesn't run through it although there may be a connection.
I would say it was much more likely that dirt or lack or lubrication kept the drive engaged. The only regular electrical problem I see that could cause this would be a sticking ignition switch helped by a big wad of keys. While the sticking could be intermittant the feel or lack of spring tention to the run position, should be noticable.
Bosch Master, ASE Master, L1
33 years MB technician