There are 2 below and 2 on top, I believe the one you are talking about is the top left one (Looking at it from the front). It's the same size as the others, 8mm socket. It's in the same location as the one adjacent to it, it's just deep in there. I would recommend a deep socket 8mm and a 3 inch extention along with your socket wrench. Shine some light in there and you'll see it right away

Best of luck!
P.S. If you don't mind me asking, what are you replacing it with? What are your plans for audio upgrades? I'm a little curious
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1995 Toyota Camry V6 LE-6M1 250K Miles, Fun Car
1997 Acura RL-Gone
2007 Acura RL SH-AWD, Technology Package, Opulent Blue Pearl- Fun Car/Daily Driver