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1969 Rear Defroster Wiring

mnewell337@gmai

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Can anyone explain to me in simple terms the idea behind the wiring for a rear defroster?

The same piece of wiring to the rear of the car transitions from a 2-wire connector (black wire & white wire), to a single black wire that connects to the rear defroster blower.

Is the white wire some kind of resistance wire?

Do both the black and white wires under the dash connect to 12 volt power?

Mike
 
Yes, up to 69 the rear deffog blower system got a resistor wire for the low speed. From 70 this changed to a dual regular wire up to blower to coil resistor mounted in a PCB and inserted into the blower housing to keep it cool, just like the AC/Heater system down the dash.
 
Nacho,

Does that mean that both wires are 12 volt, and with the switch in the low speed position, power is sent through the white (resistor) wire which results in a slower blower speed, and when the switch is in the high speed position the power is sent through the black wire for a faster blower motor speed?

Mike
 
Yes.

When is set the low speed the power flows throught the wire resistor, then to the only path (spliced into the single line) up to blower.

On high speed the resistor is bypassed thought the straight line to the single path up to the blower.

8B538631-DC66-4547-BD32-6C52EED1DCCB.jpeg


can’t talk about the voltage result throught the resistor.

on laters, both lines run up to blower and are sent with full voltage on every stage, but the resistor attached to blower is the one what cuts the power. Then after the mounted on resistor the blower is fed.
 
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