Where are you going to? other side of the truck or in the bed?
Good question Duffil. 2 gauge is great for a lower resistance drop across a much longer distance, such as under the bed.
But keep in mind, you want to use a braid of wire with as many individual wires as possible to spread the current load which will result in less heat buildup and therefore less resistance.
If the 4 gauge wire you have has triple the number of individual wires than the 2 gauge wire you have, then I would use the 4 gauge wire.
But really, just moving to the other side of the engine compartment won't require too critical a discussion here.
BigMike
