[Trevor]

Don't start hacking into the existing loom and messing up your car. As previously suggested, run a separate wire from the battery positive, with an inline fuse close to the battery terminal. You advise that you will only be connecting low current devices, in which case a 15 amp fuse will be ample.

If you wish to do a flash job and anticipate connecting devices drawing fairly heavy current, use say a 12 gauge wire and 30 amp fuse, run to a multi fuse block within the car. You can then protect each item individually with lower rated fuses as suitable. There are fuse blocks available with convenient terminals, for separately connecting whatever 12 volt D.C. appliances you wish. This is often referred to as a fuse splitter.

The short wire from the inline fuse to the battery is not protected, which is the very reason for keeping it short, as well as away from possible contact with ground.