I have a car Fiesta 1.3 Endura 2001 – 2002.
It is fitted with a Ford CD car radio.
Up until two days ago the car radio worked fine (and it still does ).
Here's the problem; –
about 18 months ago the rear screen heater stopped working.
I looked at it and couldn't see anything obvious. I checked the
connectors and the switch and the fuses. put to one side to do when I
could fit it in.

On Saturday I got the workshop manual out and the multimeter. 10 minutes
late I locate the problem, the relay which is mounted up behind the fuse
box appears to not work. Upon examination of the relay the high current
terminal has overheated and gone open circuit. Cleaned up and swapped
that relay for another one of the same type mounted in the same fuse box
checked circuits and it's okay.

Later that day I go to Tesco's and radio isn't working very well, low
signal.
I think to myself that's funny! Just out of interest I turn off the rear
screen heater. The radio now works. So I turn the heat back on again,
and the radio goes hissy, turn it off and the radio is fine.

I've rechecked that the rear screen circuits are all intact and not
arcing or anything but it got me beat (that's not hard).
Any ideas ?