2000 CHevy blazer 3rd brake lite problem...

Howdy all,
I have a 2000 Chevy Blazer. A little while back, my 3rd brake light, hich mount trailer brake light, went out. I checked the fuse, but it was good. Is
there another fuse that effects this brake light? Both my other brake lites work fine.
If there is not another fuse in line, how do you change this lite? It goes into the blazer with out having a plug on the outside. Do I have to remove the headliner to fix this problem?
Thanks in advance!
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