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SOGL V0.12, 73 71 70 66 bytes

.”L7:±¹‘Ο4↕ooā.⁾ Y*¾(){"}^ņF⁵),WοΓy⅜¬κ8ΕL▓‚7m~Ε⅝Γ‘7n┼F (=f⁄2=+⁽{@┼

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-4 bytes by looping over a string like (YYY) like the Charcoal answer

63 bytes would work if 2 didn't need to be handled :/

Python 3, 200 195 191 190 186 bytes

d,*l=" _%c_     , [___]   , /:' \   ,|::   |  ,\::.  /  , \::./   ,  '='    ".split(',')
x=int(input())-2
print(' '*3,-~x*'.--.__.--'+'.\n',d%'(',d%'Y'*x,d%')')
for s in l:print(s,s*x,s)

-1 byte from dylnan
-4 bytes from Rod

Takes input on stdin.

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Explanation:

d,*l=" _%c_     , [___]   , /:' \   ,|::   |  ,\::.  /  , \::./   ,  '='    ".split(',')
# d is the second row, without the (, Y, or ) to connect the light to the strand
# l is the third through eighth rows in a list
x=int(input())-2
# x is the number of lights in the middle of the strand
print(' '*3,-~x*'.--.__.--'+'.\n',d%'(',d%'Y'*x,d%')')
# print x+1 wire segments and a trailing dot, starting four spaces over
# on the next line, print the connectors, _(_, then _Y_ * x, then _)_
for s in l:print(s,s*x,s)
# on the Nth line, print the Nth light row, a space,
#     x * the Nth light row, a space, and the Nth light row

Additional Festive Version!

Pyth, 113 107 bytes

+"    ."*=tQ"--.__.--."++"  _(_ "j"_Y_"*Q]*6d" _)_"jms[d;jd*Q]*2;;d)c5" /:' \ |::   |\::.  / \::./   '='  "

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Not exactly the golfiest version...