Heater (blower) blows instrument light fuse, and heater fuse has no voltage at all (no matter ignition switch position). It also seems that bulb test (brake, coolant indicator) do not work. Ground and/or ignition switch problem?
If the blower is blowing fuses then I'd say your blower motor is bad or one of the resistors is bad, probably the motor. I don't think there is a common path to the instrument panel. Have you checked the flex circuit on the instrument panel and lights for a problem?
Sometimes when the blower motors get old and start to go bad they burn the contact plug on the firewall creating a high impedance issue and in turn that creates more heat and can corrode and contaminate the contacts. Find that plug and clean it then squeeze it a little for a better contact or replace the plug.
thank you Pete, good guess is much better than nothing. I check blower motor by connecting 12V (16A fuse) from to battery blower switch (brown lead). No problem, motor is ok, but...
voltage on that brown lead from fuse box? to blower switch is 0-12V (same as instrument lights). The fuse that blew was for instrument light.