TOM H. - If the wire running from light-to-light is small, the left light would be dimmer than the right, I'd use a minimum of 16 Ga wire on all my wiring, and 14 is better. Most of my wiring work gets 12 ga now, I bought a roll around work bench & storage cabinent from work that came with several THOUSAND feet of different colors 12 Ga MTW wire... all for Ten Dollars.
Also check the head light panel to make sure it's tight, vibration can kill lights quick like that. You know all those Chevy p/u's, late 90's vintage you ALWAYS see with one burned out frt parking light? I read a little blurb in a magazine years ago, the "molded grill" is too stiff, transmits too much vibration and a new bulb will fail in minutes on rough roads. Took GM until the next model change to fix it. Once the grill cracks, both parking lights last forever.
FWIW, on my old '96 F250, in 17-1/2 years, and 301,600+ miles, I've replaced one head light element, both license plate lights due to corrosion, and about two dozen clearance light bulbs on the cab roof. Quite a change from my first car, '70 Chevy Nova, sealed beam head lights last six months at most, always carried a spare with me. Same deal as the Chevy trucks, vibration.