Not to be rude but I have a Sony head unit that is only making sound out of the passengers door speaker and it is driving me nuts! I figured the amp was bad and the replacement did the same thing. Would my next step be this test as well? I tested the 4 channels with a test light at the connectors where they had wired in the adaptor plug and it lit up on all 4 channels. Is that where you are saying I should use a "test" speaker? ON the radio side of the plug? I dont know why but I assumed that if the test light lit up it had to be power but now I am back at square one. Or do I cut the wires on the other side of the plug or closer to the amp? I am looking for a speaker now . .please advise and excuse the highjack. Thanks again for any help and I will be following this post closely.

I have been reading the best bang info and then the new guy that had a few different ways to improve on that mod and I am willing to go with the 4 channel hookup also, I just checked and my Sony CDX GTS6UP has tons of adjustments and pre outs .. etc that I know nothing about but I will figure it out . When I was reading people kept changing how to get the 4 channel so if there is a way that you know will improve the sound then I want to set mine up that way to. I will go back and see if there was a final way that everyone agreed to and use it. Thanks