To heater blower only works when on level 5. When the blower is not on level 5 the ABS and parking brake warning lights are on I also get message to service 4 wheel drive. I had the blower resistor replaced 3 years ago. And the mission switch was just replace by mechanic a week ago. From my understanding both of these could be a problem. Which issue you do you think is most likely causing the lights as well as blower issue. Faulty ignition switch or another bad resister
If you take an ohm meter and check voltage at your 30amp fuse in fuse block left side of dash for heater. With key on and heater fan switch off you find that you do not have a full 12 volts. So you need to replace your ele ignition switch.