On an E body with rear defrost.

How is the the rear blower wired from the dash mounted switch ?
Which side does said wiring run down the car ?

I have the switch and the rear blower housing and fan assy.

In my service manual there is nothing to go on.

Also, I've seen some rear defrosters with a resistor mounted on the hsg. But the assembly I have there is no resistor
,, should there be ?

two piece wiring harness running down the drive side rocker panel. The resistors showed up in 1972 models to help heat the air.

Where does it plug into the main dash harness ?
And if no resistor how does the 2 speeds work ?

The back of the switch has three prongs (male) and the plug has a black, white and green wire. Black and white go to the motor and the green plugs into the green three way on the main harness.

well crap, that means I'm missing a harness from the switch to the rear blower

Thanks

If you send me a pm I have a complete assembly out of 71 charger I can take some pics of the harness and everything if you want.

They were all 2speed, varied how that was acheived. Earlier year cars 1 of the wires going to motor was a resistance wire (low speed), other was full voltage (high). Therefore no resistor at motor. Later, that wire become non-resistance & resistor mounted at motor gave low speed. Because it becomes hot, it was placed in the air-flow to cool it., not the air.

If you don't have the resistance-type wiring, you will need to mount a resistor.

Most of that wiring is hidden from switch to where enters trunk. You can use twin-wire (like a lamp cord type) for inthe trunk. But color coding may not match the original. The plug ends are nothing special.

Ok, my next question, is how and where does it neck down to a single plug for the motor connector.

Switch has 3 plugs, B+ in and 2 seperate B+ outs, depending on speed selected.
Yet the motor itself has only one single spade connector.

I have a wiring harness schematic for a Fury and it shows a diode/resistor in the circuit ?

Not sure I understand why one circuit would not feed both circuits regardless of which speed is selected

Here's a pic from 70 valiant manual showing wiring.

I'm making my own wiring, does anyone know if the resistance wire is something special or is it just a standard 20 guage copper wire?

Hi Bill, hope this helps

I should have an extra one of these if you're not in a rush

Depending on the type of defogger motor assembly you have, there will either be a single wire to the motor or a circuit board resistor mounted on the air plenum. Here is a picture of one defogger motor assembly with the circuit board resistor. All of the wiring mentioned below was stranded, not solid copper.

The single cable versions used an overall cable length of 12’ 6” with a male T connector to plug into the dash harness adapter that Vlad (Hey Vlad!) is showing plugged in at the kick panel. A black 18 gauge wire on the – T and white 20 gauge wire on the | T. That taped two wire harness ran for 8’ 9” and then were crimped together with a black 16 gauge wire that was 3’ 7” running to a single female terminal to the single wire male wire from the defogger motor.

The dual cable version used the same length, but was a Siamese cable with both the black and black w/ white stripe being 18 gauge with T connectors on both ends. A male T at the kick panel and female T at the defogger motor assembly. The solid black wire was on the – T and the black w/ white stripe on the | T male connector at the kick panel. On the motor side the wiring was inverted and the Black w/ White Stripe was connected on the – T and the Black was connected on the | T female connector.









Jim

Thanks a bunch Jim! Exactly the info I was looking for! I've got the underdash wireing, so for me it's just the 12' 6" single cable I need to make. Thanks again

I've made the wireing like described today (single contector at the motor). Could not hear any significant difference in speed between the two speeds. Can anybody confirm that there should be/should not be much difference?

I can hear the difference in speeds in mine. Performs roughly same at both speeds: lousy and almost worthless.

Yes, there is not as much of a fan speed difference with the single wire defogger motor as compared to the resistor mounted on the plenum housing.

Attached is the only occurrence that is shown in a 70 Plymouth service manual that details the wiring for the single wire version. The wiring gauge sizes are correct. When testing the impedance difference on the single wire motor end harness, setting an analog meter to read 0 Ohms between black and the motor end will show a -3 Ohm loss reading between the white wire and the motor end.

With the "improved" version defogger using the resistor mounted on the plenum housing, the circuit board shows a -10 Ohm difference for the low speed compared to 0 Ohms for the high speed. It is much more apparent that there is a speed change. This same resistor cicuit board is what was used for the two speed fan positions on non A/C E body heater boxes.



Jim