Wiring a Teknosha Primus brake controller

I want to wire in my brake controller into the trunk of the SAAB. There are 2 40 amp circuits that were for the factory amp that are not used. I'll tap the brake light as the trigger. That way the whole thing can live bake there when not in use and I can bring it into the cabin when needed.

My question has to do with the instructions Teknosha provides. They say you have to wire directly to the battery or the unit might not work properly. They are particular about the ground.

So my question is, can I wire it the way I want as long as I make sure I have a solid ground connection? I haven't poked around, but there should be an acceptable contact back there.

Thoughts?

Its been almost a year since I installed my P3 so my memory of how I did it is a little foggy but it is always powered until inactivity causes it to go to sleep. I'm guessing a circuit for subs is switched when the key is off. I'd follow their instructions and run another wire if you have to.

I've installed a few brake controllers and always ran a power and ground from the battery, to the unit, then to the connector in the back.

Im confused by your plan to leave it in the back until it's needed. Are you going to have a loop of wire and bring it up? There should be a connector on the unit so you can wire it up proper and put it in the glovebox when not needed.

Thanks for the feedback. Mostly me being lazy and not wanting to run wires through the firewall. Yes, the idea was to create a cable that would bring the unit up into the cabin through the ski pass through when in use and store the unit and wires in the side compartment in the trunk when not being used.

My Prodigy is hooked to the junction block on the firewall (which has a lead to the battery) and is grounded on the firewall as well. Has been working just fine for 3 years like that.

It is powered all the time but goes to "sleep" until you touch the brake pedal.