Its been a couple of years since I replaced mine, but I believe there is a sequence to which of the 3 lights you have to put in first so they will fit together. Like I said, its just something i think i am remembering. I would loosen all the nuts first and then see if you can get them to move around and fit. If that doesn't work, take the nuts completely off, try to get them all alligned together. If your original lights fit fine, then your probably just not getting the pegs aligned with the holes in the header.