I have a 2004 3.2 8p. RHD.

The cigarette lighter port does not work.

I took it out and put a multimeter on it and it reads 0.36v.

Fuse 24 is a red 10 amp fuse on my fusebox, so I tried changing that for a 20 amp fuse and a Headlight level warning came up on the dash. So this led me to think perhaps I got the fuse wrong but all advice online keeps saying 'change fuse 24'

There are three wires on the plug that connects to it; I could only get that multimeter reading connecting as seen in these pics, otherwise it read zero. (This was with the car ignition on)

Any help, greatly appreciated.

Hello Michael,

Never, ever replace a fuse with a higher rated one. The correct fuse rating has been chosen to protect the circuit. 
Kind regards,

Gareth. 

I suggest you use your multimeter to test the voltage at the fuse holder and the resistance of the wire between fuse & lighter.

Hello Michael,

You seem to have posted your plea and not returned to view the responses. 
We trust you are OK. 

Turns out I replaced fuse 24 and all is good. Fuse diagram confusing as car is RHD but understand it now