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Ignition switch is source of high speed relay ‘coil’ terminals power along with the blower switch while the actual load power is hot all times - anytime relay coil closes the blower turns on - regardless of key position. High speed blower is on a separate circuit all together - rest of the blower speeds are controlled by the blower motor resistor which is powered on by ignition switch and selected by blower switch. Relay replacement should fix this problem. Link posted is video of relay replacement procedure.