i wanted to swap out my old headlight for new ones. and side marker lights. but every pair i find have 2 slots for the actual light. but i only have 1 light and one slot in the headlight. so y do all the new ones i have bin looking at end up having 2 slots and not 1? any body help me out here? thanks

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iv got a 94 ford ranger. most baisic truck u can ever get. no power stearing. manual locks and windows. got a JVC KDR200, with a pair of Pyle 6" X 8" Blue Label 3-Way Speakers and wired an antennna. its a 2.3L 4 banger, with a 5 speed manual transmission. it had 117,400 miles on it wen i got it. i plan on dropping it a few inches. in the procces of repainting the interior. i want new headlights and taillights and paint my factory rims black. plan on getting a cheap sub and put in it.