There's a number of odd electrical issues in my 03MY 4.4 Vogue SE...

The PDC doesn't always come on when hitting reverse - sometimes it won't even come on with the manual button
Sometimes when I put the radio on, the volume is at 0%
Dashboard screen "flickers" now and again, though it all works perfectly
Very occasionally, when I try to start it, it's like a flat battery. If I try again straight away it *will* flatten the battery but if I turn off, wait a moment, then try again and i'ts fine.
Left hand front heated seat won't come on - the button light flickers on then off again
Left hand read heated seat won't come on - the button light flickers on then off again
Left hand headlight washer doesn't move

Someone mentioned checking the earth points, which I *will* find time to do, but are there another thoughts on this and if any of these might be connected?

Also getting trans failsafe mode under erratic conditions. Tym
(current) L322 3.6 TDV8 Vogue 2008 Tonga Green
(previous) L322 4.4 LPG Vogue SE 2003

If it sticks, force it. If it breaks, it needs replacing anyway.

battery on the way out? Might be worth checking if it will hold a full charge. in My experience multiple elec errors always lead back to a dying battery as the issue.

is your battery the original 03 factory fit. if so - bit long in the tooth now.

might also be worth checking alternator charge is as it should be. 405 AB exec seats Baltic and Cirrus
93 RR Classic efi

Remember it's easier to get forgiveness than permission!

Gone in order:
4.4 TDV8 SE - gone to a good home
93 Classic hard dash Plymouth Blue
03 L322 Oslo Blue
2000 Disco TD5 ES Epsom Green
98 P38 Rioja Red
89 Classic Cairngorm Brown

Have you checked to see if the pdc sensors themselves are actually working? Put the car in reverse with the ignition on and then put your ear to each sensor in turn, they should emit an audible click.
My radio does that occasionally, I have no idea but it works otherwise so I've just left it alone.
The screen flickering does seem to suggest a bad connection somewhere.
Your intermittent starting problem to me suggests a possible problem with your ignition switch. This could possibly explain your screen flicker problem.
Heated seats not working could possibly be problems with the seat power plugs or simply the seat elements have failed.
Headlight washer problem is probably down to a u/s wiper motor.
I'm not so sure I would worry too much about the earths on these cars I get the impression they are usually non problematic.

When they work the PDCs are fine. Its just sometimes they don't come on. Bearing in mind I have erratic "fail safe" issues on my gearbox I am presuming its all electrically related!

Think the battery is fine as I left my dashcam on for a few hours the other day and it started fine afterwards (also left sidelights on!) Tym
(current) L322 3.6 TDV8 Vogue 2008 Tonga Green
(previous) L322 4.4 LPG Vogue SE 2003

If it sticks, force it. If it breaks, it needs replacing anyway.