I have been trying to buy a good used W123 back glass with a good defroster locally and trying to tell the seller how to determine whether the defroster is good or bad turns out to be not so easy. The electrical connections to the defroster grid on the glass is not accessible without a lot of work- the 2 panel trim pieces on the C pillars (seat belt runs through it) has to be removed and doing so may break the 3 plastic hook/ clips, especially in cold weather. Not advisable IMO.

The easiest way is to measure the current to the defroster. You will need an ammeter that can measure to at least 10 amps.

1. Remove fuse 10

2. Clip one ammeter lead to the lower spring contact of fuse 10. Make sure meter is set to the correct amp scale and the leads are plugged into the correct socket on the meter. My meter has a separate socket for the 20 amp input that is different for volt and ohm measurements.

3. Clip the other ammeter lead to battery + terminal

4. Push the defroster toggle switch to turn it on. If the light on the switch lights up, it is working. Now go read the meter! A good defroster should read a little over 7 amps.


This test takes just a few minutes. Key is not needed since you are supplying power directly to the defroster circuit, bypassing the accessory relay.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Another way, if you don't have an ammeter:

Remove the driver side lower dash cover
Unplug the big C104 connector.
The C104 is the one with the tail going toward the back of the car, don't confuse it with the connector for the turn signal switch which looks similar. It is easy to tell them apart because the tail of that connector goes up the steering column.

Once you have C104 apart, check between the pin side, pin 14, to ground. You should have about 2 ohms if the element is good.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Thank you. Pictures really, really help. I'll go to Autozone tomorrow to see if I can rent something like this (I need to have the Corolla scanned anyway... the low idle problem persists... sheesh...).

I'm also looking at checking out an automotive electronics book out of the library so that I don't end up in this situation again, trying to talk stupid to someone who speaks knowledgeable .

__________________
"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

Steam up the glass on a cold morning & power the defroster, you will soon see if all the elements are working. Take a pic as proof.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Not sure if Autozoo rents DVMs. Go to Harborfreight and buy this for $5.29. It has a 10A input.

http://www.harborfreight.com/7-function-multimeter-98025.html

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

nice tips, funola and jay_bob. an ohmmeter uses much less power than an ammeter so for convenience and safety i think the C104 suggestion is a good one.

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'77 240D, 504H, OM617.952, etc.

Layback suggestion of steaming up the window is good. this way you know if the whole Grid is working.

I have a spare window I was thinking of steaming up and applying 12v directly to it to see if the whole Grid works.

There is/was a kit with the paint to touch up any Grid lines that do not work.

The HF DVM is easy to get for free. just look for their sales flyers and there is always something for free. One being a DVM.

I now have 26 sitting on a shelf. Hey, they are free.
this is not counting the ones I have in the vehicles and gave away.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

Can you post a picture of the connector and also the relay? The reason I made this DIY is that I want to make it easy.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Sorry I don't have my 123 any more, sold it to Greazzer...

There is a photo of it in the 123 ETM but it looks like those pictures of UFOs as seen in the rag papers in the checkout line.

Maybe vstech can get a shot of the under dash of a 123. He's got a few available...

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

You're worried about how much power the meter use?

As for safety the meter should be fused. The only thing you should be careful of using the amps scale is to not short the probe to ground when the other probe is connected to battery positive.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I drove up to Joosepi Luna's this past weekend to buy his back glass with a good defroster and took this pic before cutting the glass out with a knife. The current is 7.41 A for a good defroster.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

FWIW, I got a reading of 7.04 A.

__________________
"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

My meter could be off, or yours. Probably mine since it is old.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked