700R4 lock out???

[naystcb]

I just finished a SM420 to 700R4 conversion on my 1971 C-20 Longhorn and everything seems to be working fine and shifting great, my question is what is a Lock Out switch for? I seem to have overdrive, it kicks down into the passing gear on the freeway and then I am cruising at 75 at 3200rpms! Do I need a lock out switch? I have no idea what it's purpose is! There is an annoying clicking clacking sound coming from the torque converter at idle, any idea what this may be?
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