Golf Mk5 Heated rear screen not working

[Rainbowchaser]

Hi,
Can anyone offer any suggestions as to why my rear screen heater will not work?

I can connect a slave battery to the heater element and it works fine

I have a positive supply to the nearside element strip and can trace this across along each of the thin screen elements to the offside and it remains positive all the way.

I've replaced what is called the radio amplifier box attached to the boot lid from the scrap yard so cannot be certain it's 100% but seems odd that 2 units are faulty

I've removed the under dash relay and tested this is working correctly.

From what I've done it seems there is no ground/earth going to the right hand element strip. If it connect a fly lead to this strip and the boot lid earth the element heats up fine.

There are two heavy brown wires that feed into the amplifier box the light brown carries positive when the switch is turned on but the darker brown wire doesn't seem to carry any positive or go ground at anytime.

Does anyone know what the dark brown wire is supposed to do and could this be my problem for the screen not going to ground??

Thanks for reading this and hope you can help

Ed

[Flash2]

Hello Ed, welcome to the forum.

The heavy brown wire is supposed to be the heated rear window earth. Check the wiring in the rubber tubing on the passenger side between the car body and the tailgate. I'm sure you'll find the heavy brown wire will be broken in there.

Jim.

[Rainbowchaser]

Hello Ed, welcome to the forum.

The heavy brown wire is supposed to be the heated rear window earth. Check the wiring in the rubber tubing on the passenger side between the car body and the tailgate. I'm sure you'll find the heavy brown wire will be broken in there.

Jim.

Hello Jim,
Thanks for the welcome and most importantly your correct diagnosis, absolutely spot on, the wire was indeed broken.
It's been frustrating to follow through the diagnosis as I kept getting odd results when testing with the meter, the broken wire explains why they varied.
Thanks again
Ed

[Flash2]

Glad I was able to help, Ed.
I meant to say in my last post...well done in your diagnosis of the fault. Your diagnosis was spot on and I'm sure you'd have found the broken wire yourself anyway. You were almost there. The radio amplifier adds a slight complication to an otherwise very simple circuit.
At least it was the brown wire that had broken on yours. It gets a bit more complicated when it's a few of the many white ones that break, trying to figure out which while wire should connect to what.

Regards.

Jim.

[Rainbowchaser]

Hi Jim,
I'm not sure I'd have ever thought that a wire of that size would break, clearly my wife has done far too much shopping and opened and closed the boot far too many times in the life of the car!!

I was headed towards grounding the screen and bypassing the amplifier box altogether as we've been driving around without the amplifier box fitted to the car and not noticed anything wrong with the radio signal.

Just in case anyone else is also seeking this solution I found lifting the rubber cover needed to be done from the bottom edge of the car body as this clips into place whereas the fitting into the boot lid is a push in grommet arrangement that is easily pulled out.

Have to say I was amazed at how many white wires there are and fully understand the challenge in repairing any of these that break.

Without your fantastic help I was lost. THANK YOU AGAIN

Ed

[dkw]

Hi
problems in this area are usually associated with the near side tailgate wiring loom. The rubber expandable boot is too small for the number of wires that pass through it and over time the wires get twisted back next forth with the hatch being opened. I think it is design fault and VW should at least contribute to a repair. The wires eventually start to break and the largest ones the brown earths break first.
push the two locating ends of the boot to one side and lift gently. You should just about see if the wires are broken.
let me know what you find. I squeezed a tube of silicone rubber into the rubber hose and I think this will cure the problem of twisted broken wires.
VW are not interested and want the customer to pay for everything. It is interesting to note that new VWs have a much more flexible rubber boot that is perceptibly larger in diameter to avoid this problem in future. So if according to VW IT IS NOT A PROBLEM WHY HAVE THEY ALTERED THE DESIGN. All down to their arrogance really.

[Rainbowchaser]

Hi,

Thanks for your response.

I did find the broken wire and repaired it. Everything has been working well for over a year now.

Fingers crossed it'll stay that way

Thanks again