For your 200w amp 10awg copper is more than enough.
If your going to add to your system later then 4awg copper will supply everything that the rangers electrical system can produce and then some.
You wont need anything larger unless you upgrade your alternator.
"Playing it safe" with larger wire is sort of a contradiction. Big wire usually goes hand and hand with larger fuses. Fuses which provide less protection because they are more stout and take more current from a short to blow, which means more electrical force that is able to cause damage.
to play it safe you would buy the wire that is the proper size, and choose a fuse that is just barely large enough to supply the needed current.
Toreador Red 05' FX4
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