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^Ditto :p There are more and more factory h/u integrations now, but one of the easiest and cheapest is the PAC Trunkloc ;)
And then setting the amp is the same using a dmm and the tutorial in the faq section

not true.
you can use a LOC, such as the PAC OEM-1, or JL Audio's Cleansweep, or the Audiocontrol version, which is a much better option than using high level inputs on an amp

Hate to bring this back up, but how do I calculate if I'm using line level inputs on the amp? My gf refuses to change her deck because she likes her factory dash. So the only option I have is to feed speaker lines into the amp.

Thanks.

Cargodz: The gain control is for matching the max HU voltage to the amp. I would personally set the gain than use attenuation in the HU for the sub out.

[quote="solacedagony"]That said, the answer to your question is obviously the marketed specs for amp output.[/quote]
:thumbsup

[quote="jjohan35"]I have a few more questions. Do I use the watt RMS numbers on the speakers or the amp?

example 1. Say I have a 75 rms x 2 ch amp, used with 100 rms speakers. Which numbers do I use?

example 2. Say I have 300 rms output on my mono amp, used with a 250 rms subwoofer. Which numbers do I use? Thanks![/quote]
^This is a perfect example of the idea

In example #1 with a 100w rms speaker and a 75w rms amp you would use the rms of the amp as it is well within the safe range of the speakers

In example #2 with a 300w rms amp used with a 250w rms sub you would use the rms of the sub... because in this case if you were to use the amps rms you would be overpowering the sub
:thumbsup

So what should I do?

I ask because cargodz formula says to multiply watt rms with ohm, then square root it. Which RMS numbers do I input into the formula?

[quote="jjohan35"]I have a few more questions. Do I use the watt RMS numbers on the speakers or the amp?

example 1. Say I have a 75 rms x 2 ch amp, used with 100 rms speakers. Which numbers do I use?

example 2. Say I have 300 rms output on my mono amp, used with a 250 rms subwoofer. Which numbers do I use? Thanks![/quote]
Since this came up, I just want to explain speaker power handling a little bit to you. The numbers that marketing uses to quantify a speaker's "power handling" are based on a certain set of criteria. Speakers have thermal power handling and mechanical power handling. Really, your "power handling" number would be the lower of the two. But what size box are the speakers? Is the pole ventilated enough for cooling? What crossover point is being used? All of these things affect power handling.

That said, the answer to your question is obviously the marketed specs for amp output.

I would also like to add that a test tone is 100% duty cycle. Music is not. So by setting gains with a multimeter and test tones, you're selling yourself short on the available power (or even setting the amp to clip, if underrated).

I have a few more questions. Do I use the watt RMS numbers on the speakers or the amp?

example 1. Say I have a 75 rms x 2 ch amp, used with 100 rms speakers. Which numbers do I use?

example 2. Say I have 300 rms output on my mono amp, used with a 250 rms subwoofer. Which numbers do I use? Thanks!

Yes you can :)