what does it do? I have a 350 turbo w/ shift kit, manual valve body, stall converter ,extra clutches and what not ,trans was professionally built and used just for drag race.
Do I need to hook it up? or not and why?

The TV cable on a TH350 is more commonly called the kickdown cable, it's what forces the downshift when you step on the gas. With a normal valvebody you don't need to connect if it you don't mind always manually downshifting. I don't know how it will work on your manual valvebody.

This is very different from the function of the TV cable on the 700R4, which must absolutely be connected correctly.

so it doesnt have anything to do with line pressure?
its only function is to pull a valve to drop to lower gear?

Line pressure in the TH350 is controlled by the vacuum modulator.

alright thanks, I was told that with the manual body that I did not need to hook the modulator and it has a plug in the spot for it.
I was just wondering about the kickdown I guess I dont need that either.

I think in manual valvebodies like yours they just max out the line pressure and eliminate the vacuum modulator. I can't imagine what the kickdown would be used for.

Could this cable be the reason my transmisison wont shift under hard acceleration?

Yes. Without the kickdown it will not downshift by itself under throttle.

It sounds more like he's having an upshift problem, not a downshift problem.