Yesterday my wife's 2007 Cherokee had the drivers side tail light go out.  Easy fix I thought.  So I took the bulb out, it looked fine.  I decided to put that bulb in the other tail light, it worked.  So I thought it was a wiring problem.  I searched and searched, nothing. Then I decided to put the original bulb from the passenger side in the drivers side, it worked.  So at this point I'm really confused.  I swapped the two bulbs over and over and they both worked in the passanger side but only the original bulb from the passanger side worked in the drivers side.  I can't figure it out but I left the bulbs where they worked so it's fixed at least.  I just thought this would be a good puzzle to figure out.  

I work on 900 series 5 tons. They have warning lights that flash on the dash board. The Original bulbs work great in them. The replacment bulbs have the same part number but a different manufacturer. When I attempt to replace them with new bulbs it wont fully light up. The coil gets alittle red but won't fully illuminate. What I found out was that the solder on the bottom of the bulb wasn't the same length allowing for a partial connection of the light. So when I replace them I add a dob of electrical solder and file them to fit. Not an ideal repair for a simple bulb change yet I dont have many other options. This is something to check out.