Radio voltage
 

I am tuning my amp and need the voltage at max output. Does anyone know the output voltage for the factory radio. Not the voltage from the alternator.

There's a lot of factors to consider. Is your factory head unit ML or non-ML? Are you tapping into the factory sub wiring, or the wiring for the door speakers, etc?

I assume you are referring to an aftermarket amp that you are adding. The factory head unit sends a digital signal to the factory amplifier under the front seat, which powers every speaker. Since there's so many variables involved; peak voltage isn't reached until a particular channel output is maxed from the factory amplifier, what you're using for a music source, etc., then ideally there's a little legwork you may want to consider for best results for your application.

But first, if you don't have a meter, and let's assume that you know the exact RMS output of a particular channel of the factory amp. For example let's say it's 30 watts RMS, and you know the speaker it is driving is a 4-ohm speaker. Let's also assume almost zero resistance in the wiring between the factory amp and the speaker. Do some math:

P = V²/R

P = power/watts. R = resistance. Since we've established that we know "P" is 30, and "R" is 4, we have this:

V²/4 = 30

To solve for voltage, P x R = V²... 30 x 4 = V². So 120 = V². The square root of 120 is ~10.95 V.

The only real way to get a real-world actual voltage rating is to play music or generated tones from a quality source, turn the volume up until it is just below clipping, then measure your speaker wires or RCA's with a digital multi-meter.

If you're using a high level input on the aftermarket amp, then there's not much else to do, although your signal will have some degree of noise to it and you'll most certainly need to turn the gain up on the amp. This is not ideal.

A slightly better solution is using the low-level preamp on the new amp and going to RCA's using a passive ($10-$20) line output converter. This may clean the signal up a little bit, but it could also provide a little too much voltage drop, and can still sound "muddy" through the new amp. The best solution is to use an active LOC, and use a DMM to verify yourself what your maximum RCA voltages are before sending it to the amp. It's the best way to keep noise out of the signal to the amp and get a wide range of adjustment.

Most modern aftermarket amps have 4-volt or higher RCA inputs. The idea is that you want (in most cases) to try to get your max RCA voltage sent to the amp at max volume close as to the rated max input of the low-level amp inputs without going over.