Firstly sorry about the basic question but i'm worried about frying something!

I fitted a new Sony head unit to my Hilux Surf some time ago without too much trouble, I just used a Toyota - ISO and then a ISO - SONY connector.

However I recently bought a GL701 for my carputer project which I want to mount in the second DIN bracket above my Sony headunit. How should I go about powering this? Can I simply split the +12V cable and the ground cable inbetween say the ISO connection and the Sony connection and use these to power the screen and the headunit?

Also, I presume that i'll need to uprate the fuse too? (Which I presume can be found in the regular fuse box?)

I would rather not power it from my carputers PSU for 2 reasons, firstly I don't have my carputer made yet and secondly my PSU is likely to be quite far away from my screen and it would be much easier and neater if I could power my screen from the wires already running in and powering my head unit.

Thanks