Q: blower motor stopped running on 2004 Mercury Grand Marquis

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Blower motor stopped running. Blower motor and blower start relay appear to be ok because blower runs when I jumper hot side of blower to plug in wiring harness and ground side of blower to ground. Is problem likely to br EATC unit or is there something else in blower circuit that can go bad?
(2) Answers
(2) Comments
You have a blower speed controller that will cause a blower to stop running if it's faulty.
This is apparently a common failure on the Automatic Climate Control models.

The repair is cheap, but it's a bit awkward to change. Your failed part is most likely the blower resistor module (Ford part #8W7Z-19E624-A) under the hood near the firewall. It is tough to even see, let alone get to. As installed, it essentially faces the rear of the curbside valve cover.

We fixed my son's with a cheap $5 part out of a junked Town Car, but I didn't want a factory part so I used an aftermarket part off Amazon (Standard Motor Products, part #RU-572, A/C Blower Motor Switch). Both cars are working fine.

There's a good video on YouTube for how to install this part (see "2003 Ford Crown Victoria Blower Motor Resistor Swap"). The job does not especially require a lot of skill to install, but definitely some patience to wiggle it into place. (HINTS: 1) Disconnect battery, drain some coolant, and disconnect your heater hoses before starting and 2) Don't reconnect your electrical cable until the part is in place)

Good luck!