I suspect your heater core has started to leak more due to moving heater hoses around during your harness installation. When heaters leak bad enough to fog to windows, it is past time to replace it. Breathing antifreeze vapors is a sure way to get real sick or die if you breathe them long enough.
It is my understanding that ethylene glycol junks your kidneys if you get enough of it into your body. Bypass heater core or replace it.
Or make sure you have good health insurance and maybe funeral arrangements.
Good luck,rcs