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Old 01-16-2020, 04:11 AM   #1
koenb
 
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Default Heated Rear Window Wiring Adaption

I've noticed my cargo van with no rear windows has the heated rear window option H22. Seems pointless, but makes me wonder if all of the components are installed in the van? How is it even an option for windowless cargo vans.

I've come across the plug (no switch) behind the dash. The wiring diagrams for this system show relays and a control module. Not sure if those exist, and I am feeling unmotivated to go outside in the cold to inspect under the seat for them.

Are there wires running from the module to the rear door contacts? I would think I could use a SPST fog light switch plugged into the rear defrost connector, same pinout as defrost switch, re configure the 16AWG wiring from the switch to bypass the module and supply 15amp fused power to the rear cab to power rear fog/backup lights. I know MB isn't keen on installing extra wiring if the option wasn't selected, but my gut thinks they might have. The lights i'm considering would only draw about 3 amps, so I would drop the 15 amp fuse down to a 5.

Thoughts? Any one out there tried this or something else? I know running separate wires, relay, fuses and switch is probably easier, but i'm up for a fun challenge.

Last edited by koenb; 01-16-2020 at 04:15 PM.
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Old 01-16-2020, 02:22 PM   #2
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Default Re: Heated Rear Window Wiring Adaption

Quote:
Originally Posted by koenb View Post
... I know MB isn't keen on installing extra wiring if the option wasn't selected,
...
Yep.

Take a look at how many contact buttons you have mounted for the rear doors. The NAS aka NAFTA driver side (right) needs 2 ea. for the license plate lamps. Additional buttons on that side would be for the heat. The passenger side door doesn't need any buttons unless there is power locks, then 2 ea. there would be for the optional heat.

That above said, I suppose that the wiring could be buried in the pillar.

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Old 01-16-2020, 02:37 PM   #3
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Default Re: Heated Rear Window Wiring Adaption

Power door locks will have four pins on the rear passenger door.
My cargo has both rear windows, defroster grids, and power locks.
I believe I have 1 of 3-pin on the driver side (license lamp and defogger share a common ground) and 2 of 3-pin on the passenger side (power lock pins span two pin blocks)

I’ll confirm today and update this post if required.

The driver side hinge was seized when I bought the van, and the defrost pin has at some point made poor contact and arced, heated up, and melted the plastic block - another reason to keep those brass pins clean.

-dave

Last edited by Nautamaran; 01-16-2020 at 02:48 PM.
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Old 01-16-2020, 04:20 PM   #4
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Default Re: Heated Rear Window Wiring Adaption

I mean MB did run the wiring for the switch in the dash. And I remember having an unused contact on my rear doors. I'll double check tonight. The option is also on my data card. I would think the rest of the system, window element excluded, was installed.
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Old 01-16-2020, 04:37 PM   #5
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Default Re: Heated Rear Window Wiring Adaption

If so, youll find a single switched/fused conductor in the tail feeding an extra pin pad on the frame contacts.
I havent looked, but expect the ground runs to the lug up in the passenger side roof ledge area?
Its -25F here in Calgary today so my usual curiosity is absent, otherwise Id check for you...

-dave

Last edited by Nautamaran; 01-16-2020 at 04:47 PM.
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Old 01-17-2020, 01:36 AM   #6
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Default Re: Heated Rear Window Wiring Adaption

Here are my rear contacts looks like 1 of 3 buttons is not used. Ignore the additional set on the passenger side door, PO installed for an extra lock. No wires that I can see on the door side, got too cold to dig further inside the pillar. Is there a way to add a button or swap the assembly to utilize the existing contact plates? My plan is to install these in the doors. Using the contacts would solve the problem of wiring into the door.
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File Type: jpg IMG_20200116_191602767.jpg (73.2 KB, 33 views)
File Type: jpg IMG_20200116_191607000.jpg (52.5 KB, 32 views)
File Type: jpg IMG_20200116_191552211.jpg (58.5 KB, 31 views)
File Type: jpg IMG_20200116_191557607.jpg (48.4 KB, 31 views)
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Old 01-17-2020, 03:22 AM   #7
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Default Re: Heated Rear Window Wiring Adaption

The door-side pin bodies have clips running parallel to the long edge. You can compress these clips by poking a pair of small screwdrivers or similar tools into the small slots, then pull the pin bodies out of the door.

The frame-side plates have not yet revealed their secrets to me... I suspect something like a putty knife is involved?

-dave
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Old 01-19-2020, 09:56 PM   #8
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Default Re: Heated Rear Window Wiring Adaption

Made some discoveries today. I checked around under my seat and found the 30 amp B+ fuse (green, slot 37), the relay (position 6, confirmed wire colors). I also think I found the module attached to inboard side of the relay holder bracket, a snapped a pic of the part numbers. Looks like another relay and holder but some of the wire colors matched, but couldn't confirm a couple of them. Does anyone know for sure what this is? See pictures. Or, if there is someone out there that knows where the module would be? When I looked for it in section 8W it says it is near the rear of the vehicle, but diagram 8w-48-4 shows the module grounds at G202 under the seat.......

Which leads to the finding that there is a grey 16AWG wire connected to the center (#2) frame contact plate, as Dave mentioned. I didn't get to test for voltage yet, but that is my next step. I believe I will need to jumper pins 3 and 7 at the dash switch plug and I should see 12v at that frame plate.

I think this means all I need to run aux backup lights is two, 3 pin door switches, a fog lamp switch, a smaller 5 amp fuse to replace the 30amp, and a little bit of wiring in the doors to make this all work. Still confused as to why this option was even selected for a windowless cargo van.

Quote:
Originally Posted by Nautamaran View Post
The door-side pin bodies have clips running parallel to the long edge. You can compress these clips by poking a pair of small screwdrivers or similar tools into the small slots, then pull the pin bodies out of the door.

The frame-side plates have not yet revealed their secrets to me... I suspect something like a putty knife is involved?

-dave
Dave, Thanks for the info on the door side switch removal. Also, I figured out that the frame side contact plates are released from the backside with the tail light removed by depressing the little tabs on top and bottom.
Attached Images
File Type: jpg fuse layout.jpg (133.0 KB, 19 views)
File Type: jpg Rear contact plate.jpg (89.3 KB, 19 views)
File Type: jpg maybe module.jpg (180.9 KB, 19 views)
Attached Files
File Type: pdf window defogger.pdf (392.4 KB, 5 views)

Last edited by koenb; 01-19-2020 at 11:56 PM.
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