Wiring Harness Issue

I have a 2002 GMC Jimmy SLS. I recently went out and bought a new deck for my truck, a Sony CDXGT430IP. I purchased a wiring harness as well for the deck, wired everything up and thought I was good to go. My only issue was my truck came with a factory 6 speaker system. The harness only had hookups for 4 speakers, as well as the deck. The guy at Futureshop said it would work in my truck, but it doesn't. Can I upgrade my system, or is my current setup as far as I can go?

So your saying that only 4 of the 6 speakers are working, or none of the speakers are working?

None of the speakers work. I have power to the deck, but nothing through the speakers.

What I would do is return the wiring harness and get yourself a 9volt battery and a cheap volt meter.

First use the volt meter to identify your constant power,ignition power, and ground. Tape and mark these wires. Next use the 9volt battery to pop the speakers to identify FR,FL,RL,RR and whatever other speakers you have. Label these wires as well.

Lastly, before you take your wiring harness back use the diagram on the packaging to match up the appropriate wire from the deck to you vehicle.

The only other option is to buy a 6 channel amp and rewire you speakers.

So what do I do once I figure out which speaker is which? My harness still only supports 4 speakers.

speakers 5 & 6 are probably just tweeters in the dash, if that's the case they are connected up as part of the front door speakers

are you sure the internal amp on the CD player is turned on

Still no luck yet. As far as I know the new deck I bought doesn't have an internal amp.

then what are you using to power the speakers ?

Is it possible there is a factory amp in the vehicle and you don't have the remote (Power antenna lead on the harness kit connector) power lead connected to turn the amp on?

As far as I know the deck is supposed to power the speakers. Im not running an amp, but the factory stereo is a Bose premium deck with a built in amp. Im not sure what else to do. I appreciate all the helpful responses.
LGE-LG830 AU-OBIGO/Q05A1-3.8 MMP/2.0

APW is saying that often times in these premium factory systems the amp is a seperate box. If that's the case, you will need to either bypass the factory amp or figure out how to turn it on.

Oh yea, and the outputs from an aftermarket deck may be too much for inputs of the factory amp to handle.