I have a pioneer rec. vsx-515. I do not have the instructions how to hook up the main sub woofer that plugs into the wall

any will work go to best buy

There should be two jacks on the back that say SUBWOOFER in the "preout" section of the back panel that is directly above the speaker jacks. Either of these jacks should work for your sub hook-up. Also make sure that you set your front speakers to small in the speaker setup menu, otherwise there will be output to the subwoofer jacks.

Hissing? How loud? A sub isn't even capable of making high frequency sounds at normal volumes.

The Pioneer manual would tell you how to enable and test the subwoofer output.
Page 17 and the MACCV procedures on Page 33 (auto) or 43 (manual)

Maybe you could name the subwoofer model so we know what it needs for input.

And we need to be careful with the indiscriminate use of the word 'power' in audio discussions. There's wall power and there's amplifier (audio) power.

In the case of subwoofers, some are self-powered (AC power cord plugged into the wall and an amplifier built-in; usually receives subwoofer-specific audio program via RCA cables from YOUR source); others are passive (just get audio power from YOUR amplifier.

if using a sub out cable to a powered sub,you have to go into the reciever menu and turn the sub out on

Hello,
The subwoofer is totally independent from your Pioneer VSX-D412. You can check if it works like you did with a finger on the hot point of the RCA cable (not very good test, as you will hear noise and can't say if that means it works OK) or better connect a known receiver to the speaker connections in the sub and test to see if it’s working properly.
Regarding the receiver, you may not have enabled the VSX to output to the sub. Read the manual on how to check for that. Only Dolby Digital 5.1 signals will allow the sub out, in a receiver of this level. It normally will not let you use the sub in stereo mode. Some more complex units will allow you that, but I believe not this model.
Good luck

problem with connection

Connect the input from the powered subwoofer to the rca jack on the VSX-409D labelled 'sub woofer preout'.

I got the same issue. But, I go ahead hooked it up two banana plugs on teh VCR outlet. It works fine on my Cerwin Vega Sub.

If I am not mistaking here, you need a self powered subwoofer to use with this unit. Those are line driven outputs for this unit. Make sure there is a wall plug on the sub that is plugged in. Good Luck