I have two inexpensive 3 bulb light fixtures in my bathroom. The same bulb (on the end) kept burning out in each fixture. When we finally quit replacing it, the middle bulbs in each fixture eventually burned out. Now one end bulb in each fixture is, and had been working fine. Is it due to internal wiring of the fixture? Seems logical to me but I'm having a problem finding anyone to agree lol
1The enemy of most light bulbs is heat. Unless you have associated blinking or other problems, it is hard to see a likely wiring based failure mode where a bulb would work for a while but burn out prematurely. Are you using incandescent, CFL or LED bulbs? Can you upload a picture of the fixture?– manassehkatz-Moving 2 CodidactMar 30, 2021 at 18:40
I may not agree with others but many times it is the connection to the lamp that is the problem. The center conductor getting folded down a little more than the others and the lamp arcs until it no longer makes a connection.
I would try (with the power off) to lift the center tab a little. These tabs are many times brass and they do have some spring to them.
A kitchen knife to lift it up a little like 1/4” so it makes a solid connection may be the fix you need to have lamps that last closer to the same life time.
1That's a great fix and has worked many times for me. I've had bulbs last longer that are close to AC vents and last shorter that were close to outside venting.– JACKMar 30, 2021 at 18:49
I have had this problem in the past. I agree with @Ed Beal's Answer (socket) and @manassehkatz comment (heat).
When I have had this problem, I noticed that sometimes it was simply a cheap light bulb. (Not always, but sometimes. And, I have had cheap bulbs die in one socket but not the other).
Sometimes, it was the wiring. (Note, this is not just the wires themselves, but also the connections and locations of the wires). Is it Aluminum wire or copper wire? (Copper is better).
Does the wire seem thin/brittle or is it firm/sturdy? Is the wire solid or stranded? (Sometimes it's solid wire in the wall and stranded in the fixture. That makes the interconnection easy to mess up.)
Are the wires all jammed into the J-Box, or is there some extra room? Jammed wires can easily "wiggle" while (re-)installing the fixture.
Are the wire nuts the right size? Are they connected properly? (Can you pull them off without twisting them?) Are all 3 sockets wired individually to the load (causing 4 black wires in the J-box: 1 for the load and 1 for each bulb), or are they connected internally and only 1 connection to the load (causing 2 black wires in the J-box). More wires on 1 connection => more potential issues.
Are the wires pinched when the fixture is attached to the wall?
Is there a ground wire in the fixture? If so, is it connected properly?
Are there other fixtures connected to this one?
Being an engineer, I "doinked" with all of these. Probably 3/4 of the time, Checking these things (magically) fixed the problem. If this did not fix the problem, I would replace the fixture with a different one -- unless, of course, the Mrs. really liked it, then I re-wired it with sturdy copper wire, quality sockets and good bulbs.
In one particular case, I had a 6-bulb hanging lamp and the bulbs lasted about 2 months. After re-wiring it, I hadn't replaced a single bulb in over 4 years (then I moved).