12V rocker switch

[bcguy]

Hello: I would like to connect my composting marine "air head" fan (small computer fan) to a rocker switch right at the unit. The pics attached show 2 thicker wires and the 2 thin air head fan wires. Should I replace "thicker" wires with same size as fan wires? The wires shown are spliced into the pos/neg wires running down the length of the hull. How should the wires then be attached to the rocker switch. thank you, much appreciated

[bcguy]

All done.... but thanks anyway