My passenger side low beam head light is dim. I changed the bulb and still have the same issue. High beams are ok. Has anyone ever seen this before and if so what was the fix?
You probably have a poor/corroded ground on that side. The extra resistance in the circuit reduces the voltage to the bulb. Electrical people call this “dropping” voltage.
Find the ground wire to the lighting harness and be sure it’s clean and well secured. You can probably get a wiring diagram (different from a schematic, it’ll show you where the wires physically run) from the dealer’s parts window for free upon request.
Or, the connector might be dirty. That’ll drop voltage too. Get some “contact cleaner” from radio Shack and flush the connector out.
Its going to be in the primary wire to that bulb. If it was the ground, both the high and low beam would be dim. But it is a poor connection. You will need a wiring diagram to find it, but it could be the connection right at the bulb where the low beam wire is attached to the terminal in the plug.
KIA has a very good warranty. Bulbs are not covered but connection problem might be. The worst they can do is say no.
I suspect a poor connection too. The first thing I’d do – after cleaning the 3 visible prongs so they look like bright new copper, is look at the face of the connector the visible prongs plug into. Are there any brown or black burn-like marks? That’d be an indication that connector needs to be replaced.
It’s always a generally good idea to remove the battery negative connector when working on the electrical system. Some newer cars however don’t take kindly to this unless the ECM’s memory power is preserved in the meantime, so find out if this is an issue before disconnecting the battery.
I recently got a 2011 Optima and the headlights are extremely dim. Ever figure out what was going on?
Lots of people have this problem with Kia headlights. The only fix I found was replace the lens unit. It seems that the reflective coating fails.
Agree. Had a friend that is a mechanic check my passenger side headlight on 2011 Kia Optima as light was dim and dangerous to drive at night without High Beams on. No issues with ground, wiring or bulb. Chrome reflective coating was deteriorated and laying in a pile inside the housing for the bulb.
I realized this thread, replied to last 4 hours ago, was old when I saw my post to get contact cleaner at Radio Shack. 
Radio Shack is only a sweet memory now.
When I looked at the dates I realized it was years old.
Its’ an easy mistake to make, ringsethj. I’ve had to discipline myself t o be very aware of dates.