From a purely electrical perspective, I'm pretty sure this will work fine and won't cause any issues. That being said, I wanted to get some more experienced thought.
In my vehicle, I have a 125A fused feed from a distribution box in the trunk (where the battery is) to a auxiliary distribution box roughly 3 feet from the center console. It gives me 3x20a always-on, and 3x20a accessory-on feeds into the console. None are in use currently.
The wire from the trunk to the box is listed as 6awg. The wiring to the console for all aux power is listed as 16awg, but seems more like 18awg.
Question 1.) From my general electricity knowledge, 6awg doesn't seem big enough to be rated at 125a. Paired with the seemingly small wires for the 20a circuits I am slightly confused. Is there a reason these seem awfully small for their circuit ratings? I don't understand how they would handle that ampacity.
Question 2.) Bear with me on this one... I think the 20a circuit wires are awfully thin for their rating. If I have something that draws 15a, would combining 2 of the always-on circuits in parallel cause any issues? Assuming of course that the aggregate circuit is safely fused and I combine them on something like a bus bar?
Question 3.) Expanding on the last question, if combining two of the circuits in parallel would work, could I then have a single 30a circuit?
The only issue I can forsee is with a load greater than 20a. If a single one of the two 20a circuits had a fuse blow, the load would be across the remaining circuit and it's fuse would also blow at that point. Inconvenient sure, but is it something that would be unsafe or unstable?