300CE heated rear window not working

[Tomkinsm]

Hello everyone,

Its that time of year when you need to demist your car. This being the first winter that I've had my 300CE-24, I switched on the heated rear window, only to find that it doesn't do anything! The light in the switch works, and the fuse is ok. From looking through the threads here, I need to check that power is getting to the screen, and that the connections are good - if these are ok then its probably the relay unit. The window is a little blown in the corners - could this be a problem? Also, can anyone tell me where the connections to the heater element are so that I can check them? Do they connect at the top or the bottom of the screen? Which pieces of trim should I remove to get to them?

Thanks for any help! I want to be able to see behind me this winter!

Mark

 

[television]

The cable comes from ECU N10 pin 6 black and white, goes through to boot with tale lamp cables etc. there is a plug in the boot X18 in the harness it is an 8 pin plug Pin 2 and 5 are the wires.

Malcolm

 

[Tomkinsm]

Thanks for this information - I'll have a look at the weekend and report back. I guess I can just put a mulitmeter on the two pins and make sure I am getting power to it? Can I also check the integrity of the window element as well?

 

[c13tay]

Multi function relay - take it apart and look for dry/broken soldered joints - cured mine and took a couple of mins - wish I hade checked that first on mine, spent weeks following wires etc !!!!

 

[Tomkinsm]

Thanks

How can I identify this relay? Haynes manual or car manual don't mention them.

 

[c13tay]

Not sure about a 300 but on a c class its in the relay compartment under the main fusebox in the engine bay. Remove the 6 or so screws that hold the fuse tray surround on and you cant miss it. lots of "normal" sized relays and a bloomin great big one - thats it

There is a thread on here somewhere wich has pics of the type of damage to the soldered joints that you may find inside the relay

 

[television]

it is N10 module in fuse box, black box nearest screen, think it is pin 6 black and white cable

Malcolm

 

[Tomkinsm]

Thanks for your help.

I checked the relay today, and no dry joints or anything appearing failed. Relay clicks when I switch on the hrw.

Having looked in the boot, I can't see any connectors or any wires going anywhere near the rear window. However, under the rear seat (passenger side) there is a large electrical unit with several connectors in it. Is this what you are descring Malcolm?

Still can't see where any wires attach to the screen - do I have to remove the parcel shelf?

What I want to check is that power is getting to the screen itself.

 

[television]

all I know is that the cable for the demister leaves the rear light harness with the 8 way plug X18. I do not know If X18 is in the boot ( I would have thought so) or under the back seat. Can you trace the cables from the rear lights back, you should then find plug X18.

Malcolm

 

[turnipsock]

Have you checked to see if there is any voltage at the rear screen?

If you have a meter, you can measure the voltage by touching the wire elements on the screen. It should be 12 volts at one end.

 

[tom7035]

Have you checked to see if there is any voltage at the rear screen?

If you have a meter, you can measure the voltage by touching the wire elements on the screen. It should be 12 volts at one end.

Mark can't find where the wires are attached at the screen end turnipsock, I can't help there.

 

[c13tay]

Just for info, my relay also still clicked and the switch light came on but no HRW.

Still put money on the relay - do you know anyone else with a merc, you could try their relay to prove the condition of yours

 

[Tomkinsm]

Thanks Television and Turnip,

I think the X18 is the one under the seat. There are a number of plugs under there and they go through to the boot. I'll try to check that one.

I think I need to remove quite lot of trim in order to get to the wires that attach to the screen, Turnip.

If I find that the screen is broken, I might just leave it. I've heard many horror stories of Autoglass and such people fitting new screens that leak, or scratching bodywork in the process. In actuall fact the dehumidifier in the air con works well to prevent demisting.

 

[Tomkinsm]

Interesting C13. I couldn't find any breaks in the relay, but the proof of the pudding would be trying a new relay, but unfortunately I don't know anyone who can lend me one.

 

[television]

You do not need a relay at this stage, you have found the 8 pin plug,pin 2 and 5 are for the screen, turn the demister on and you should have 12volts at 2 and 5 alternativly you should have 12v on either 2 or 5 to ground (chassis) if you have then it will be the screen, if you have not it is the relay or wiring.
you can put an Ohm meter on the wires that go up to the screen, and it should read almost zero ohms.
If you find that the screen is open circuit there are some repair kits on the market. If you look very close you should be able to see the break.

 

[Jim Gallagher]

Hrw

I am with the Relay MB P/N 210 821 00 47 being faulty.

The heated window, assuming it was working normally last time is reliable, unless it has been damaged. I had the same problem last year and replaced the Relay- problem solved.

Interestingly, my wipers and HRW stopped working within the last week. I was pricing a second hand realy on ebay, but meanwhile took out the Relay rubbed the terminals, took out every fuse and cleaned the fuses at each end. Result-Wipers and HRW working. Not sure what solved the problem cleaning fuses or Relay. I will buy a Relay and keep as a spare.

 

[shirubaby]

Thanks Television and Turnip,

I think the X18 is the one under the seat. There are a number of plugs under there and they go through to the boot. I'll try to check that one.

I dont think the X18 is under the seat. In a 300ce there are two vacume valve units with six vacume tubes (underneath the passenge side rear seat). There are also 2 electric connectors going into these valves.

Underneath the drivers side rear seat, there is a sodding big vacume pump that works the central locking...It has 2 electrical connectors and several vacume tubes connected to it.

Well that's what I've found in my 300ce

 

[shirubaby]

I think I need to remove quite lot of trim in order to get to the wires that attach to the screen, Turnip.

You dont need to remove anything. If you slightly pull back the rear piller plastic trim (from the inside of your car of course)...you can see the tabs that connect to the heater elements in your screen. There is one tab on either side of the car....about halfway down the side of the screen.

There should be 12volts between these two tabs.

Checked mine today and found that 12v is present...which means that the heater elements are broken....bugger

Any ideas?...apart from replacing the screen?

 

[television]

There are a lot of kits on the market just type in "heated rear window repair" and take your pick

Malcolm

 

[merctronic]

or with a test light accross the live and earth terminals