1952 Mercury Blower Motor Wiring



The heater blower motor on my 52 Mercury is not working the way it is currently connected.

This is the wiring currently:

Three wires are coming from the blower motor - 1 is connected to the negative terminal on the coil and the other two run back to the switch in the car. The switch in the car is fed in the center by a fused wire from the ignition switch.

When I disconnect the wire to the coil and both wires that are connected to the switch at the dash the blower works by touching the wire that had been connected to the coil to the negative (hot) terminal of the battery and one of the other two wires to the positive (ground) terminal. If I switch between the two wires that touch ground the motor runs at high or low speed.

I hope this makes better sense than my original version.


Your post is totally confusing. Please proof read it and make corrections.


Yes. Unconfuse the post. And realize that Fords with 6 volt batteries had POSITIVE grounds.


This is how a 58 Ford blower motor is wired, they didn’t change much from year to year back then.



First off, suggest you not involve the coil when doing this experiment. It’s tough enough to solve elecgrical problems without introducing add’l components into the circuit. The negative terminal of the coil on a points-type ignition system sometimes is connected to ground via the point contacts. In that case the fan wouldn’t run at all. When the point contacts are open though it will measure close to the battery voltage, but there’s a current path through the coil involved. Not a good idea to power the blower fan through the primary of the ignition coil. That’s too much current for too much on-time, might burn out the ignition coil. Plus you’ll likely get a big spark whenever you disconnect it.

I don’t know how the 52 Merc heater blower is wired, but on all of my vehicles tI’ve ever owned, there’s a fused battery + circuit which goes to the heater fan resistor block, and the switch you use to set the fan speed selects from among various points in that resistor block (a network of resistors) , and directs that particular selected contact point to the + of the blower. For high speed, it is just the battery + that is selected. For slower fan speeds the path goes through some of the resistors. Usually the path that burns out is the one for the slowest fan speed. That’s b/c the power is divided between the fan and the resistors, and at slow fan speeds the most power goes to the resistors and the least power goes to the fan. The blower negative is connected to chassis ground.

If you measure the voltage using a volt meter between the fan + and chassis ground, it should be battery voltage in the high speed setting, and a lower voltage in the slower speed settings. What voltages are you reading at each fan speed setting when you measure between those two points?


I’m sorry for the confusion.

Does this diagram refer to a 12 volt negative ground system or a 6 volt positive ground or would it work the same for both?

The only reason that a wire is connect to the coil is that this seemed to be where it was connected when I got the car. Would it hurt anything to ground this wire to the body of the car? There seems to be current feeding from both directions the way it is currently hooked up.


Is your car positive grounded? In that case maybe the coil negative isn’t connected to the points, instead the coil posititive is where the points get connected. In that case you may be right that the heater circuit is getting one side of its power from the coil negative, b/c the coil negative is connected to the battery negative.

How many wires go into the blower motor? Does one of them obviously connect to the chassis?


Yes, this car is still 6 volt positive ground.

There are three wires coming out of the blower motor. One is connected the negative side of the coil and the other two run back to the switch on the dash. There is not a wire on the motor obviously connected to the chassis.


The blower motor is never intended to be hooked to the ignition coil. It does not matter whether it is 6V +gnd or 12v -gnd. Its acc position on the ignition switch to the blower switch. The two wires from the blower switch to the blower motor. The ground wire to the frame.


So I should be safe connecting the wire that was on the coil the the frame of the car and the other two run back to the switch?


You are feeding -6VDC to both sides of the motor, it won’t run that way. Take the wire off the coil ad connect it to ground. Or the center wire on the switch could be connected to ground, check that first. Sometimes the switch is on the ground side.


Yep, I definitely get that now.

I think the middle wire on the switch is supposed to be the hot wire as it has a fuse between the ignition and the switch.


Reading your edited post. Take the wire off the coil and ground it.


Will do. Thank you!


The way it was connected before you started working on it, when you say it didn’t work, how exactly did it not work? When you turned the switch to fast or to slow, did it not run in either position? And the fuse remained ok no matter what the switch position was? Or if not that, what?


Nothing happened at all. The fuse did not blow and the fan did not operate.


I’ve got a 52 Motors book but there is absolutely no wiring information in it for the blower. If it were me, I’d pull the blower and the switch and put it on the bench to figure out which wire is what and what works and what doesn’t. All you need is a power supply like a battery charger.


Grounding the wire to the body of the car that had been connected to the coil resulted in a properly functioning blower motor. Thanks for your help, everyone!


My guess is the wire connected to the coil is the ground for the motor, & should be connected to the chassis, and the other two are for the power for the two speeds; i.e. when the fan is turned on, one or the other has voltage on it, but not both, depending on the switch position, negative voltage in this case presumably, as referenced to chassis ground. But the advice above to remove the motor and the switch from the vehicle and test it on the bench is where I’d start if I had this problem. If you’re not electric-experienced, just take it to an auto-electric shop and they could figure it out on their bench. The problem might be the motor winding is just burned out. You’ve verified the motor turns freely by hand, right?


Looks like Keith was right on. Man would positive ground be confusing.