troubleshooting heater blower motor

[1973fordf100]

I have added factory air from a 78 f100 to a 73 f100 wiring harness everything is working except no current to heater blower motor, have taken heater core & blower motor out. there is a small harness left of heater core area go through firewall all I think are black one is I know a ground other two I don't know. is this the power supply source to blower motor.

[jzjames]

One black and one orange?

[1973fordf100]

One black and one orange?

I know that but where is power supplied from for the heater blower motor

[DuckRyder]

On a bump side it goes through the blower motor resistor which is in the heater box IIRC...

[1973fordf100]

I know what the black & orange wires are for I need to know where the power is supplied from. Is it the wires that go through the firewall left of the heater box which are all black I think ? I don't have any current going to the heater motor.

[DuckRyder]

We don’t seem to have a wiring diagram for a 73 only 72 (which is a bumpside and not a dentside) and a 74 with is a dentside.

http://www.fordification.net/tech/image ... r_4of8.jpg

[1973fordf100]

still trying to find out where the heater blower gets it 12 volt current from I know then wires to the motor are black & orange.& there is three wires going through the firewall left of evaporator & heater motor where do they hook up to 1 is a ground I think one plugs into the compressor. One more round black male end on it.

[sargentrs]

With our without A/C? If A/C equipped, there may be an additional circuit in the Heat/Defrost/AC selector switch that disconnects power to the heater when in A/C mode. Comparing that '74 diagram DuckRyder supplied and '72 diagram from the tech section,there seems to be a common theme that I have no reason to believe would vary all the way up to '79. All diagrams point to the blower getting it's power through the fan switch and heater controls which get their power from the ACC circuit of the ignition switch. Main harness 14401 branches over to the fan switch which leads to the blower resistor which leads to the blower motor. In that '74 diagram connector chart you'll find connectors #604-#607 and their locations. These most likely control the heater/AC circuits. Check them to make sure all are connected and the wires are in good condition. The way it works, the key is on or in ACC position which energizes the circuit to the fan switch/controls. The control levers position determines whether that power is routed to the blower motor and the A/C compressor clutch or just the blower motor. Those switches are actually on the A/C housing itself, on a bumpside that is. The current from the fan switch routes through the resistor in the heater/AC unit housing which controls the operation and speed of the motor. First check the operation of your fan switch. If you think it's faulty, they should be readily available from the usual vendors.

[1973fordf100]

need to know where heater blower gets it 12 volts from the brown & orange wires from the motor to where The three black wires left of heater motor & heater core go where 1 is a ground 1 I think plugs into compressor 1 has a round type plug which is male.

[DuckRyder]

I’m not trying to be rude here, but we know you are trying to figure out where the blower motor gets power from, we are trying to help you even though most of us don’t have a dent side truck.

You are going to have to start answering some of our questions and perhaps post a picture of what you are dealing with. Do the black wires you have found have any stripes?

If you open the link to the wiring diagram I posted up, at the bottom it describes the connector wire colors and general location. (incidentally you can go to other pages by changing “4of8.jpg” in the URL to 5 and so forth)

Have you located the blower motor resistor?

[sargentrs]

This is for a '69 but is an excellent example of how the heater gets it's power from the circuits I referred to above. http://www.fordification.com/tech/wirin ... heater.jpg It gets power from the heater resistor via the heater fan switch. This one shows equipped with A/C. http://www.fordification.com/tech/wirin ... g_69ac.jpg A '73 is probably very similar if not identical. May be different color wires but the design is the same. Ignition switch -> fan switch -> heater resistor -> blower motor.