Hi all, hoping for a bit of guidance.

Message popped up on the dash to check right low-beam headlight. Replaced bulb, still no good. Swapped bulbs from left to right. Both bulbs are good.

So, figured it might be the ballast. Dropped the front bumper, took both headlight assemblies out. Thought the easiest way to test the ballast is to swap left and right and see what happens. Swapped ballasts, plugged headlights back in and now they both don't work. LED running lights still work on both sides but no low or high beam.

So I removed the assemblies again swapped the ballast back and now we're back to the left low beam working but no right.

Didn't make sense to me, thought I must have missed a connection or something so I did it all again with the same result.

Any ideas what's going on? I don't understand why the good ballast in the left wouldn't work when swapped to the right.