l wanna wire a 400 watt sub to a 200 watt amp in my car but l do not know if it will work

It will be severely underpowered. You will have to run the amp full power to get even decent sound from the sub and the amp will be over run and not last long. It is better to have more power in the amp and run it at lower gains to keep it from running hot.

it will be fine, you wo not have any trouble until you hook a 400 watt amp to a 200 watt sub

It should work all right, but do not try it the other way around.

The difference between 200 watts and 400 watts is only about 3 dB of output. It wo not be ''severely underpowered''; it just wo not get quite as loud as it could with a more powerful amp. Go ahead and try it out; if it is loud enough for your needs, then there is no problem. You are not going to damage anything by matching up these two components, as long as you set the gains properly.

It will be fine as long as u adjust the gain right.

The purpose of the gain is to match the signal volts RMS coming from the source (CD player, etc.) to the input of the amp to prevent clipping (damage by over powering).

Here is a guide that will help u set the gain correctly http://box.net/shared/uchv4dbk88

You will need a multi-meter (AC voltmeter, $15 from Radio$hack), Microsoft Excel & a way to burn an audio CD from an MP3.

If u do not have Excel, use this link http://box.net/shared/nkkw1dhk4g

See my site for more info http://spkrbox1.spaces.live.com

it will sound just fine as long as you have the right size box. and go ahead and turn that gain knob up. Do not forget to buy the right wiring it is just as important.