The prefered and best way to ground anything is through the frame. I used the bracket for the battery for external lights. I don't know how high of a load your talking about, but a good rule of thumb is one gauge thicker wire than your hot lead.
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00' Super Black SE
98' Jeep Wrangler
Sport
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--The difference between a warrior and an ordinary person is that the warrior sees everything as a challenge while an ordinary person sees everything as a blessing or a curse.--