Have been having lots of electrical problems with my Ford Focus, basically i think its easier if i write a list:

At one point my car boot was just opening at its own accord while driving but has stopped now,

Always have a problem with the passenger sides front locking like not locking or unlocking in sequence with the rest of the car,

Speaker on passenger side door doesn't work unless turn music up loud,

My headlights dim when i turn on the windscreen heater (also affects the heating aswell),

Car locks try to lock and sometimes succeed while driving,

Cigratte lighter doesn't work but that dont matter.

Many thanks for any suggestions.

I wound check the health of the battery, and the earth straps at both ends of the 2 straps of braided bare conductor. The live lines can also get oxidised at the ends, and copper oxide is a great insulator.

At the age your car is, I would expect the battery would be on its last gasp. (at one time, 6 years was good service)

The posts on the battery can need cleaning with a wire brush, and re-clamped-up with a good smothering of vaseline, to prevent atmospheric corrosion. (it doesn't conduct electricity)