1974 Charger Rear Window Defrost System

[tfdub]

 Hello all.  I have a rear back glass. defrost system that I've never seen in a 74 b-body before. My Charger does not have the standard blower motor mounted in the trunk under the rear shelf that blows air up to the rear window. My car has the rear heat tape like you see in newer cars. It fits the window perfectly, does a great job of defrost and has Mopar part numbers on the switch (3746670), the switch handle (3488522) the cables (3764956) to the window heat tape. The power cables run down each side of the car and each heats half of the tape on the window. Have you ever seen this type of rear back glass defrost system before and is it an add on? I'll include photos of the parts. I'm mounting the switch to the bottom of the dash frame as I remember it - this is one part I didn't take photos of. It looks like the same switch frame the blower motor uses. The switch itself has  OFF and  ON positions. It returns to OFF as soon as you let go of the switch. To defrost the window, you must hold it in the on position and the light glows through a hole on the right side of the bezel and once the window is defrosted ( about 1 to 2 minutes) let go of plastic handle. Works great. I'll include photos.

[tfdub]

I would really appreciate it if someone who has a rear defrost system switch mounted under the dash would take a pic of it looking up from the floor. I think I know how it goes, but want to be sure. Thanks.
Terry

[Nacho-RT74]

I have only seen this system on my 74 manual parts catalog an once being sold on ebay. It was a brand new option for 74s, never before.

About the switch...it uses one screw for the switch assembly, mounting it above the sheetmetal and screw underneath, and another screw one for the bezel.

I guess there is a 3rd point for the heater on indicator light

I think you still miss the relay.

[tfdub]

So there was a relay (timer) that once turned on would stay on for a set time (like maybe a couple of minutes ) and then open up and turn off the defrost? Interesting. This is the first time I've seen this style of defrost on this old of a Mopar.  Besides the small light mounted to shine through the hole on the black plastic bezel, there's the other light on the back of the switch mount (with the orange wire in photo) that shines down through an small opening in the bottom of the dash frame. The light bulb has a green sleeve over it to light up the white printing (On OFF) on plastic bezel. That's different. Thanks.
Terry

[Bronzedodge]

The electric setup wasn't as common back then, but the early 70's is the transition from fan to electric.  I have a friend with a 73 Dart, has factory electric defrost.

[Nacho-RT74]

The orange wire bulb is to iluminate the bezel throught the dash opening like any other accesory switch used there air ram, headlights washers, regular blower defrost, rear glass on SWs. Wlll turn on with cluster lights and dimm with them. You'll find an orange rubber mold to plug that bullet terminal around heater-A/C control area. Console shifter light also plugs there.

I have the blower defrost in mine, but no pics of that, however got a nice acc switch set pic around... wil post later.

About the relay, I can't tell if is a timer or is just a relay itself. Being you describe the switch as a temporal switch which doesn't remain on, ut sounds logical it could be a timer ?

[Nacho-RT74]

I know I have a set pics of this assembly from an old members 71 R/T who sent me a CD Rom of his car, but Can't find the CD at this moment. This was saved into my PC thought

The switch assembly with lighting provision slides over the dash frame and you install the crews from bottom.

then the bezel got the provision to fit in with the switch screw there ( big hole ) and will attach to the same switch on the second hole ( smaller one ) with another screw on SAME switch bracket

[Nacho-RT74]

OK, found the CD...

this is the view from bottom. You can see there the two screws setup... one for the switch itself on dash on big bezel hole, the other for the bezel itself, both threated straight to the switch bracket... and on second pic you'll see the orange mold for the bezel lighting.

You can see there also how the switch assemblies are OVER the dash frame and just the bezel below it.

[Nacho-RT74]

I can't tell if is this relay since is listed for 75 and laters, but something similar ( I don't think too much different )

https://www.ebay.com/itm/NEW-MOPAR-HEATED-REAR-WINDOW-RELAY-OEM-3838095-NOS-/161213974779?_trksid=p2349526.m4383.l4275.c10

same unit, diff brackets shape... I think more correct to be attached to dash frame at a side of the glove box

https://www.ebay.com/itm/NOS-MOPAR-1975-7-FURY-CHARGER-ROADRUNNER-CORDOBA-REAR-HEATED-WINDOW-RELAY-NIB-/252407507339?_trksid=p2349526.m4383.l4275.c10

or this one with an extra brace?:
https://www.ebay.com/itm/NOS-75-77-Plymouth-Dodge-Rear-Window-Heater-Relay-Mopar-Part-No-4057984/152219843186?epid=1437056890&hash=item2371027a72:g:3hkAAOSwEppUR8Au&vxp=mtr


I know have seen the full package being sold couple of years ago on ebay. I thiugh had saved the pics somewhere but not

[Nacho-RT74]

Diagram section from 74 FSM for that... and it says indeed it's a timer relay. Checking how it shows wires, the light takes the power from same source to the grid, so will remain lightened on as far the grid is sourced from relay.

I don't have the FSM with me at this moment to check it, and the Parts Manual doesn't say much about.

as far I know, this is a brad new option for 74, so, I don't think 73 FSM will get info about this ( 73 diagrams are less technical and easier to understand  )

[Nacho-RT74]

althought the 74 action accents catalog says 73/74.

[Nacho-RT74]

74 dealers book catalog:



But nothing about that on 73, just the blower

[tfdub]

Thank you Nacho. It looks to be an interesting option. I was going to remove it thinking it was a later add on but it works and I think I'll leave it in. The passenger side of the window grid is grounded. I don't plan on driving the car anymore in weather needing a defroster but you never know. I'm glad I have the option in the car. The FSM is a big help I'm finding out.  Again, thank you.
Terry

[Nacho-RT74]

I'd like that option for myself, and remove the blower, being able to fit dual speakers, but they weren't equipped down here, and even If I get to find the system ( like once the one on ebay I found ), ship overseas a glass is not a guarantee I really will get it safe.

Of course the grid requires to be grounded somewhere to get the short able to heat the element on glass.

FSM is available on CD Rom and printed versions, new repros and old originals. Myself, I love the stuff in hands so went with an original old one, just that I don't have it handy. Mymopar.com got those manuals but not the 74 yet though.

Dunno if the electrical heater could be on the fender tag ? I don't think so, but if you got the Buildsheet, is G01 code

[tfdub]

Nacho, you are correct. Line 8 under section G Glass -Mirrors has Heated B/Lite  0- has a 1 under it. Very cool. I see this option requires a 65 amp alternator. I better take a look at the alternator I put in.
Thanks.
Terry

[Nacho-RT74]

upgrade the Wiring and paths for the charging system ( check the electrical section, stickied thread )

[tfdub]

Nacho, after reading the electrical upgrade you referenced in the electrical section, I studied the FSM Charger electrical drawings more and noticed the 65 Amp system has a black 8 gauge wire to the alternator instead of the standard 12 gauge wire. I checked my black alternator wire with another one I have and sure enough, my car has the 8 gauge wire. This also explains the additional red and black wires running through the grommet in the firewall (cowl) to the ammeter that I had brought up in another discussion back in September on Moparts. The FSM on page 8-221 shows that extra wiring through the grommet for the 65 amp system. I'll include a photo showing the differences in black alternator wire. I'll also include a pic of the extra wires through the grommet that hooked up to the ammeter. The FSM shows two black and two red wires hooked up to the ammeter with the 65 amp system. My Charger I'm working on has the white plastic cover. I guess I need to spend more time with the FSM. I thought all this wiring, the defrost grid on the rear window and the switches were all added later and I was going to remove it all. This shows me to use the FSM to check all the options I find on the car. Again, thanks.
Terry

[Nacho-RT74]

Damn! I never associated it was you! LOL

Actually ( per 71 diagram ) should be one or the other ( 8 or 12 gauge ) not both. Underdah harness will remain the same though, just arriving anywhere on engine bay side when running the 8 gauge section. Since my car didn't have the big one and I upgraded the alt I simply added and kept both. There is no reason to remove the 12 gauge wire unless is already damaged, but if still in good conditions both can live together. An important thing here is just use one fuse link on the side batt wire. I updated that info on my thread. So the original 12 gauge red wire can be removed and kept the big gauge one with just one fuse link... or splice both to just one fuse link ( 14 gauge ), just that splice both wires into just one fuse link wouldn't be a clean job really.

I can see some differences on 74 diagrams thought, being the 8 gauge wire spliced just right before the bulkhead to run on both paths ( grommet and bulkhead ) at the same time and getting an extra fuse link

[Nacho-RT74]

Per 74 FSM It seems 74 could run like this

I'm not sure about the red wire section between bulhead and starter relay so I removed it from diagram. FSM diagram doesn't say should stay or not when 65 amps alt

[400sforever]

My dad ordered a brand new 74 charger se back in the day. His had the defrost lines in the rear window. I have never seen one before. Must be a super rare option

[tfdub]

As Nacho said, first year option. I had never seen this option before. I almost tore it out thinking it was after market until I saw the pentastar logo on the switch. Shows I need to study the manual more. I know it works because I used it many times when the car was my daily driver back in the late 80s and the window would fog/frost up in cold weather. It also has a cloth headliner and seats of  a pattern/material I have never seen before. SMS has the headliner material which turns out was used on the C bodies but they want $375 to make the headliner. I was afraid to ask what new seat covers would cost. I'm trying to decide whether to invest that kind of money in a 74 Rallye Charger with the E58 engine option. It had a black 3/4 vinyl top and black body stripe on it when I bought it in 1987 but the tag calls out for the white top and black body stripe. This car has absolutely no body rust on it. There was some minor surface rust near the battery tray.
Terry

[Nacho-RT74]

depending on how much was the initial investment and the resto investment, being a 360 4 bbls ( Rallye by default, like 340s on previous years and not common ) could worth fill all its needs

once again, I'd love to find that defrost system and add it to my car. Venezuelan Mopars never got Fender tags or buildsheet, so I'm not slaved to it LOL