Blower motor doesn't work on high. Relay is good, blower is good. Checked blower motor connector with volt meter. Volts are good on settings 1:2:3 but I get nothing on setting 4

Have you actually bench tested the high speed blower relay to confirm it is working? HIGH SPEED blower is on an independent circuit which bypasses other speed settings controlled by the blower motor resistor. Check for open circuit (broken wire) or failed high speed blower relay - assuming the fuses have been *TESTED*..

Sounds like a failed blower motor resistor.