Dennis brought this up in another thread, but I didn't want to "hijack" that thread so I'm starting a new one. How do you correctly wire a rear defroster to get the 2 speed function? The defroster itself has only one wire leading to it (orange / black). The switch has a fat wire (white / purple) and 2 smaller wires (red) & (orange / black). I would think the fat (white / purple) is the power in and the 2 smaller ones are the high and low speeds. Where do these 2 wires go and how does it get down to 1 wire at the blower? Is there a relay I'm missing? Maybe a resistor wire?
I put one in my car using the original factory harnesses. Once lead obviously goes to the blower which is ground to the rear shelf. I also recall another plug goes to the Accessory lead on the fuse panel.
They way it works is there are 2 power wires from the switch, going to the motor. They tie in together near the motor so there is 1 power lead at the motor. One of these wires is a resistive wire. The other is a standard wire. When 12v is switch to the normal wire, all 12v reaches the motor and it runs full speed. When it is switched to the resistive wire, some of the voltage is actually dropped by the wire so the motor dosent get the full 12v. Therefore it runs slower.
wow! in retrospect, i shoulda taken the harness... at the time i couldn't be bothered to figure out how it worked. maybe i'll use a potentiometer. hmmmm. todds' car. todds' decision.
So on the low speed side, I need to splice in a length of resistor wire, eh? Any idea how long that wire is and what color it is in a harness? There are other resistor wires like for the fan blower, ignition coil, would a piece of that wire work?
The wire is about 4 ft long and is a dull red. It measures about 6.1 ohms of resistance. It drops about 5.2 volts which puts about 6.8 volts to the motor on low speed. I believe I have a couple of complete defogger set ups if anyone is interested.
Dennis, I would be interested in one for my tan Maverick. I am in the process of getting it ready as daily driver, and the defogger would come in handy. Thanks, Dave
Where does the White/Purple Stripe wire terminate? I'm sure it's the 12V supply but I looked on the fuse panel and couldn't find a male lug for this female lug to connect over. Dan would shoot me if I cut the terminal off and spliced the wire into a 12V KO source.
Rick ... I think that harness is out of a 1976 car so that connector was meant to attach to the rear of the fuse panel mounted on the dash. That is is the 12V power lead .. you may need to extend it so it can connect to the accessory area on the firewall fuse panel.
Thanks, Dan. There is a place for a fuse on the panel that didn't have a fuse in it. I pushed the lug over one of the fuse retainers. So, I didn't have to cut the terminal off. Thanks. and MAN, INSTALLING A DEFOGGER IS NOT AS EASY AS ONE MIGHT THINK IT TO BE! It's all back together now. Whew! Unfortunately, the Defogger grill doesn't sit flush with the rear deck panel. I'll figure something out on that - one day when I have absolutely nothing else to do.
Not sure how you cut your hole in the deck ... but if I remember it should be just slightly smaller the size of the grill. The bolts should not go through the rear deck tray ...
The "factory" hole for the motor was already cut in the "metal deck". Also, the holes for the screws are there also (same from-factory appearance). The grill has a shoulder on each screw tab. Those bottom out on the metal deck. I can't get the grill to set any lower (without cutting them back). I'd have to add more padding to raise the "particle board thingy" to meet the bottom side of the grill but then there'd be a 'hump' in the center of the back dash. I'll figure out something. I'm tired of working on it for now - plus I just got back from helping a buddy remove his 302 out of a Mustang. Dang, I'm old. Whew!
I hear ya ... I had a busy car day too .. I washed, clayed, polished and waxed the Grabber today getting it ready for car show season and a big show next weekend at Stone Mountain Park. Also changed the oil. Then a friend came over and we replaced all the brake pads on his Explorer. Finally I decided to replace the thermostat in the F150 since the temp guage would occasionally go up to the A in NORMAL. I put an original 195 degree in there and now it doesn't even open until it's on the L in NORMAL. Defective? Not sure ... but gonna put a 180 degree in tomorrow and try again. Anyway ... I plan on being sore tomorrow ...
Rick: Make sure the rear defrost "hot" wire has a fuse in it....or is plugged into a circuit with a fuse. You probably need some of the factory padding under the package tray in order to get the "board" to sit up high enough so it is flush against the grill. That is what I had to do to mine.
