98 Grand Cherokee 5.9 Install

I recently purchased an MTX RT202 amplifier to power a subwoofer in my 98 Jeep Grand Cherokee Limtied 5.9L with a 10 speaker infinity gold system. Because I wanted to keep the stock stereo, I tapped into the right rear and left rear high level speaker leads and remote turn on before they enter the stock infinity gold amplifier. (I connected the spliced wires to a high level speaker harness provided by MTX with the amp) I then connected the harness to the high level input on the RT202 amplifier. The result is that the the rear speakers and the subwoofer do not turn on when the car is started. Only after the car is started and the harness is removed and then plugged back into the RT202 will the back speakers and the subwoofer work. What is the problem, and how do I fix it?

You need to tap in after your factory amp in order for it to work. try that and let me know what happens

Following bberman1's suggestion, I tapped into the high level wires after they are routed through the amp.  This is the result:   When I turn the car on, the rear door speakers and sub still do not work.  HOWEVER, when I power the stereo off and then back on, the rear door speaker and sub then begin to work. 

Right Rear + = TN/RD                 Connected to Grey wire on MTX harness

From the results, I am lead to believe that the amp is not properly recognizing when there is a signal being sent trhough the wires when the car is first started.  Any ideas?

Thanks for the help so far.