New guy need help!

Just want to start off by saying that I am a new member here, and i look forward to learning alot with your help.

With that being said i have a question. I recently helped install some subb's, amp, and cap in my friends 99 denali. The problem is when you turn it up the amp goes into a ''safe mode'' a little light indacates it, and the bass just stops going through the subb's, but it hit's really good before a certain volume level on the head unit?

Here is all the info i can give you. It's a 1999 gmc denali, it has a pioneer cd player, factory bose speakers-subb still intact and working. The amp is a JL dont remember which one but I know it is a class D and one ohm stable 2 channel, the subb's are Elemental Design audio A15's in a sealed box, and it has a one farad cap. 

At first i had them hooked up for what i think was one ohm and it worked,but started right off the bat cutting off so he took it somewhere and they re-wired the subbs for 2 or 4 ohm, and said that should fix it, but it didnt. I had a friend tell me once that the factory bose systems in the older denali's wont allow much bass and thats why it cut's the amp into safe mode and the subb's cant hit. We've tried moving the ground to different spots, and nothing seems to help. Is there a product that would go inline with the amp to allow it to have the bass, and not go through the factory radio (if my friend is right)?

Sorry for such a long first post, but i hope someone out there can help.

upgrade the deck, or grab signal before the amplifiers.  Also ensure your gain settings are correct.

Thanks for the help, but I have no idea what grab signal before the amp means? Can you explain? Also he has an alpine thas a few years old should i try it and see the pioneer is causing it, or should i do somthing else?

I cant remember i'll ask him tonight , I think its a 1200 watt amp , but i dont know.  wayland1985 do you think that the cap could cause it to do this? Or that factory subb? when he had the cd player installed they put in some connector cause it has on star and bose, do yall think that could have anything to do with it?

I'll let yall know the amp model as soon as i can and start trying some of yalls tips thanks again.

Alpine Guy the gain is set at only about 1/4 up so it's not set high, and it can accually go alot higher, but when you start to turn it up (the gain), and try to turn the h/u up in volume the amp goes into safe mode and no more bass???

It's really frustrating because when you turn it up the subbs sound really good, and then you go for a little more volume (and i'm not talking about maxing out the volume), and bam it cuts itself off.

Does anyone know if that is true about the older denali's?  thanks.

Your problem is that the JL amp is only only stable for 1.5 ohms probobly. Don't ask me why JL didn't decide to make their amps .5 ohm more stable. That is probobly why, when you turn up the volume the amp goes into protect. The nice feature about the JL amp is that (if its the slash series) it outputs the same continuous power from 4 to 1.5 ohms (3 to 8 on the two or four channel amps when they are bridged). Re-wire your subs for 4 ohms (I'm guessing they are DVC 4 ohm so this should be possible).

I could have gave you better info if you would have gave me more details on the stuff he's using....

The two channel amps only handle 3 ohms bridged unless he has them running on each channel...

What is the JL's gain (volume as some people call it, even though thats not correct) set at?