2 amps, 1 signal, will one work if the other doesn't?

I am not sure. Recommend contacting a local car audio professional or Clarion customer support directly here:

https://clarion.com/xe/en/user-support/inquiry/contactus

did you run direct to the speakers or to the rear of the radio to split factory wiring. Check to make sure that you are connected to the correct side of the wiring behind the radio. If that is correct, then check the input of the amp. Try a different source and see if you get signal. Make sure your wiring is not crimped.

I use my ipod and hook it to an 1/8" x RCA splitter and plug direct in the amp. try to isolate the amp as much as possible. 1 speaker to outputs and 1 source you know works. Then test from there.

I have a Marantz 7.1 AV receiver (sr5500) and I run a 5.1 set up for home theatre and use the 2 extra channels to run a pair of outdoor stereo speakers... When I first set it up I also found I could not get a digital signal output, only analog, after reading the manual(!) I discovered that it can only output an analog signal...so I have used the phono outputs on my blu-ray player into the CD input of the AV amp and play CDs outside through this and it also outputs the optical digital signal into the AV amp through the DVD input...my iPod also plays through a dock and it's analog output to the speakers outside through another (CD-R) anolog input on the amp... Hope this helps

Make sure your audio source is playing.

Make sure your channel is not muted.

Make sure your channel is assigned to "main mix" (bottom button to right of main volume slider).

Make sure your main output slider has volume applied.

Make sure the cable you're plugging into your "main output" is being plugged into the 1/4" or xlr output receptacle that corresponds with the slider you provided volume to.

You should then put the outgoing cable into either an eq or an amp.

If you're going to an amp first, place the cable carrying the signal from the board into an "incoming" slot on the amp. Run a cable from the output of that channel of the amp to a speaker. Turn on the amp and fade the volume knobs up. That should give you power - provided your board, cables, amp and speaker are working properly.

If you're going to an EQ first, place the cable carrying the signal fromt he board into an "incoming" slot on the eq. Then run a cable from the output of the same channel on the eq to an incoming slot on your amp. Then run an outgoing cable from the same channel on the amp to a speaker. Flip your eq on, flip your amp on, fade up the volume on the amp, and make sure you don't have a gate closed on the eq (also make sure if you have a gain knob on the eq, that it's at least partially providing power). If your board, cables, eq, amp and speaker are working properly, you will have sound.

Quick and dirty way is to turn up one of the AUX channels, say #1 on the Guitar player's inoput channel/strip. Have all other AUX #1 completely CCW so none of the others get mixed on the AUX.

Use a TRS cable from AUX1 output to the guitar players monitor amp.

NOTE. The signal to his amp will only be controlled by the AUX1 on his channel AND the AUX1 Master.

One normally uses the AUX outputs for monitor functions.

Depends on the amplifier.
Some have pass-thru RCA jacks - most don't.

You can split the signal with a y adapter - however it also splits the line voltage carrying the signal in 1/2 as well.

Doing this for a sub amp? Then it wont matter as much. Split the signal at the first amplifier with y cables, and run another short RCA to the other amp.

If the amplifier has an output - use it instead - as there is no signal lost (in theory)

Thanks for using FixYa - a 4 THUMBS rating is appreciated for answering your FREE question.

Speaker output from the amplifier is a higher voltage than a preout. The speaker level signal has to be reduced to a line level signal in order to connect to another amplifier. I used a car stereo "speaker to line level adapter" and then connected a second amp to run my front channel speakers. Works just fine.

If by saying amp outputs you are refering to the RCA jacks on back of the head unit (Left and Right RCA jacks usually labeled FRONT, REAR, SUB, etc...) then you do have options even if your head unit doesn't provide a SUB channel.  These RCA jacks/amp outputs carry the signal (music or whatever) at a lower voltage (and is typically more like DC voltage as there is a ground reference which is 0 volts and signal rides on the positive voltage), providing a cleaner signal to the amp which does all the work.  The wires behind the amp that you connect directly to the speakers is typically amplified by the head unit itself and is a much higher voltage level and varies from negative to positive ( AC voltage.).

You could use the other channels (FRONT or REAR) if available, (a specific SUB amp output cuts all the higher frequencies out, passing just the lower subwofer frequencies inside the head unit).

if you want to strive for a more efficient use of your sub, use a low-pass/SUBwoffer filter (a crossover) in between the Head unit and amp, thus providing the amp with subwoffer signal, (or if for some odd reason you have SPEAKER level sub connections you can use a line output converter which will let you run RCA to the amp.)

Hope this helps u understand why I couldn't just say get a new stereo nor could I just say use splitters on available amp outs.

You will need a line level adaptor to get an audio input for the amp.

A line level adaptor is a device that lets you tap off of your speaker outputs of the radio and it converts that signal into the proper level for an RCA input signal the amplifier uses.

If you are installing the amp in the trunk of the car you can just tap off the speaker outputs of the rear speakers mounted in the trunk. Keep the speaker outputs connected to the speakers, just run an extra set of wires from them to the line level adaptor. It will not take anything away from the speakers sound because it is not a power drain on them.

After that, you just connect the power wires for the amp as you would normally and you also need to run an extra wire from the radio power antenna wire to the remote turn on of the amp, or you can use a wire directly from the battery and connect it thru a switch you would need to connect somewhere around the dash, so you can turn the amp on and off when you need to. The power antenna wire from the radio is best, so you don't need to turn the amp on and off manually. It is easy to forget about turning it off sometimes and that would run doen your battery if the amp is left on over night even with no signal going thru it.

Then connect your speakers to the amp and thats it.

Then big issue is getting an audio signal to the amp and the turn on signal for the amp.

If you need more help let me know,

Dave

What's the battery voltage across the B+ and ground terminals of the amp when the engine is running?

Does the amp go into protect mode when the engine is running?

Are you sure the head unit is still producing output when the engine is running?