Blown Fuse / W123 Heated reader window

[Servicepoint]

Each time I try to operate the heated rear window the no 10 red 16amp fuse blows. My concern is that the electromagnetic engine fan is also on this fuse and I potentially run the risk of overheating. Can anyone suggest what I can check to find the fault and perhaps eliminate whether it’s the fan or the heated window? I think the relay for the rear window is behind the instrument binnacle but don’t want to go ahead and change that when it could be something more obvious. The elements in the window appear does in ok condition. Since taking the picture I have changed all the fuses to brass.

 

[wrdcc01]

You've already eliminated the fan by the fuse only blowing when you use the HRW so I wouldn't worry about that. The Elements in the window won't be an issue either, it's going to be a wiring problem between the relay switched contact and the window. The switch just puts an earth on to the relay coil so a fault there would just mean it's on all the time. Have any children or animals used the back seat and possibly banged on the C-pillar covering? Take that off and check that the connector isn't touching the post. Not sure which side on a 123 but it's the left on 124. (Earth on the other side with just a short bit of wire bolted to the post.)

 

[Servicepoint]

I stripped off the switch and cleaned it out as it was greasy and gunged up, it appears to work better with a def action it did have previously though I’ve not put it back on.
Im not sure if anything has bumped the C pillar as I’ve only just got the car, it looks like tve back seat meads removed to remove the pillar cover?

 

[wrdcc01]

You should be able to pull the trim away and then towards the front of the car without taking out the seat back.

 

[Servicepoint]

You should be able to pull the trim away and then towards the front of the car without taking out the seat back.

Are there any particular fixings I need to correctly lever away or is it just a case of getting my fingers in behind it and prizing it away?
Do you know if it’s passenger or driver side for the connection?

edit
Sorry, I just noted you weren’t sure of the side.

 

[Jockcl500]

Are you sure that the fuse rating is correct, I thought they used a bigger amp fuse for heated rear window.

 

[Servicepoint]

Are you sure that the fuse rating is correct, I thought they used a bigger amp fuse for heated rear window.

Good point, I thought this myself but when I checked the fuse diagram in the inside of the box my understanding is that fuse 10 would be a red 16amp however rear seat heating & Aux heating if installed would be 25amp.

 

[wrdcc01]

Just had a look at a picture of the c-pillar trim on ebay and it looks like one clip in the middle and a couple of tabs at the front.

 

[Servicepoint]

Just had a look at a picture of the c-pillar trim on ebay and it looks like one clip in the middle and a couple of tabs at the front.

Thanks, I never thought to look at eBay for a picture.
I’ll have a look.

 

[Servicepoint]

Found this.

https://www.tonk.ca/models/w123/w123CD2/Program/Chassis/68-449.pdf

 

[Servicepoint]

I stripped off both C pillar covers and everything looks to be in very good condition, clean and all wiring on both sides as I think it should be.
The only thing that I’m capable of doing now without an auto electrician is the relay behind the instruments.
Can anyone advise if the relay could be at fault and cause the fuse to blow each time the switch is operated or am I wasting my time getting in behind the instruments to check / replace it ?

 

[Flyinspanner]

Yes a failed relay can short circuit.

have you tried disconnecting the fan, operating the HRW, and seeing if it blows?

disconnect HRW, run engine till fan kicks in - does it blow?

use multimeter to check wiring, is there a short?

 

[Servicepoint]

Yes a failed relay can short circuit.

have you tried disconnecting the fan, operating the HRW, and seeing if it blows?

disconnect HRW, run engine till fan kicks in - does it blow?

use multimeter to check wiring, is there a short?

Thanks.
I have replaced the fuse previously and ran the engine up to temp and the fan kicked in without blowing the fuse. I haven’t disconnected the fan and tried the HRW though, I just assumed the fault was on the HRW as the fan worked ok.
I’m not overly confident with the electrics so I’m thinking I’ll take a chance and replace the relay before resorting to an auto electrician.