I want to wire in an inline fuse for my 12v power socket

From stock the existing fuse powers the 12v supply in the dash and also an additional supply in the rear of my armrest for rear passengers

I have also wired in a twin usb port running off the 12v supply in the dash and I am also powering the monitor for my rear camera off the same 12v ssupply

All seems to be functioning properly so far but to be on the safe side I'd like to tap in an inline fuse somewhere (either on the wire running to power the camera monitor or to the wire powering the usb socket)

What ampage fuse should I tap in for the additional items? Would 5amp be enough or higher?

Depends on the current draw of the devices fitted after the fuse.have your devices got amps or watts cunsumption listed/stamped sonewhere?

This is the usb port

http://www.ebay.co.uk/itm/Water-Resistant-Twin-USB-Socket-Dash-Mount-Car-12-24V-2-1-amp-Charger-Adapter-/191302395590?pt=LH_DefaultDomain_3&hash=item2c8a82e6c6

And this is the monitor

http://www.ebay.co.uk/itm/Fold-4-3-TFT-LCD-Color-Car-Reverse-Rear-View-Monitor-For-Backup-Camera-DVD-UK-/231458159494?pt=LH_DefaultDomain_3&hash=item35e3fb3b86

should imagine the monitor doesnt use that much power so try 5 amps and see if it blows, would put fuse inline before both of your extra devices are wired in.

both are already wired in and working fine. where would be best to wire it in?

probably isnt actually needed as i only really use one 12v power socket at a time to power me satnav and the monitor only has power when i put it in reverse

but i'm just thinking precautionary if some time in future i have a car full of passengers and people in the back are charging their phone etc using the rear port and a front passenger is using a front port and the satnav is also plugged in