Help please! Odd wiring problem on my 997.1

[Roundm]

So I have a fault on my 997.1. The heated rear screen doesn’t demist. So I started to work through the problem logically,

Tested the screen for continuity having disconnected the cables leading to it. Tick reads 9 ohms, This makes the current at 12v around 1.25 amps and the element around 120W. Sounds about right to me

Check the relay under the shelf behind the rear seat - 12v on the grey/white. Tick.

Check 12v across the grey/white and the brown feeds to the screen (with the screen unplugged). Tick.

Start engine, and all of a sudden the voltage shows as 2.4v errr what ????

So only way is if something is raising the voltage on the -ve connection to around 10v or dragging the 12v supply down when the engine is running. Very odd.

Any suggestions on where to look next ? Ive heard of people commenting about replacing the earth strap that goes from engine to chassis, could that failing explain this? Wouldn’t I see this as a charging problem somehow.

Any other ideas where I can look ?

And thanks for any ideas

[AinsleyB]

Current is bleeding away somewhere, try checking the earth strap as suggested. I had a an electric issue which was traced to simply an earth strap that just needed clearing up with a file to improve its conductivity.

[Roundm]

Thanks. I’ll give it a try