got turn signals? might be wired in wrong - stop lite sw NOT going - either works or not [or sometimes, but not part way or backwards], if the brake lites are dimmer it's because you've got the wires reversed [it's the bulb elements that determine the bright/dim] - do both brake lites work w/ headlites off? does headlite dimmer sw work right?
wait - switch taillite bulbs, or replace bulb on side brake lite doesn't work [should always have spare bulb in glovebox anyway, right?], see if that helps, then fix the bright/dim problem [prolly switch wires at rear of frame where there should be connector plugs,or under cab, check the plugs that are there underneath driver side, make very sure the grounds on the taillights are solid, and the ground from frame to bed - see if it's still not right - have a stiff drink and report back in the mornin!

was this a repop wire kit, or DIY?
Bill