I have a 2005 f 150 with a factory subwooferve the factory sub plug in. Is there anyway to hook the factory sub up without having the factory sub plug in on the headunit?

 

Sure is, you need to put power to the "Enable" wire in the plug, "Shield" goes to ground, and subwoofer + and - obviously speak for themselves.

I've had mine connected for the last 2 years and operating perfectly. I provided power to it from the Radio ignition power, after playing with 5V supplies, it caused me "clicking" issues when turning it on, so I connected it to 12V and it actually worked a treat.