O.K I just helped my friend install a amp/sub in his car. I have installed many systems before but this is the first time I have used a stock deck with a HighLevel to LowLevel convertor. I followed the instructions on the convertor and it is hooked up right. Now here comes the problem the subs play very low on most songs and very loud on one certian song. Now is the convertor causing the problem. I got the crossover at about 90 Hz. I don't know what is going on here. Any help would be appreicated.

Try reversing the connections on one channel to the speaker leads from the high-to-low adapter. I sounds like one channel has it's polarity reversed.