Well , I am thinking you can if you where to plug in an aftermarket harness . You would have access to the car side of every wire in that harness , color coded on top of that . But you would have to purchase a harness and you would NOT be able to check the radio with that harness ..
If you have the Pioneer amped system , then you need to go to the speaker and not the harness behind the radio .
On the speaker leads , with a multi meter check the impedance . It should be reading between 2 ohms to 8 ohms . Dead short and the speaker is bad .
Remove the a-pillar and check that tweeter that is not playing with a multi meter . Then you have found the problem .
Chances are , you need to replace some speakers . 6.5 alpine component's are under 40.00 dollars with free shipping " factory level replacement" .
http://www.ebay.com/itm/BRAND-NEW-ALPINE-6-1-2-6-5-INCH-2-WAY-CAR-AUDIO-COMPONENT-SPEAKER-SYSTEM-PAIR-/290994828460?pt=Car_Speakers&hash=item43c0a4b4ac

 

When all I want to do is see if its loose connections?

 

The most common problem for losing sound in the door speakers is getting corrosion where the speaker plugs in to the harness. The doors get a lot of internal moisture build up. Pull the interior panels and check.

 

Animosity?

Pull the Waterfall off. Stick your fingers into the A/C vent holes and yank. The HU is sitting right there held in by a couple of screws.

 

Finally got tired of listening to just 1 speaker, so ordered 2 pair of Kenwoods from Crutchfield. Made installation easy, adapters included.

1st door panel took a bit of time, didn't want to screw anything up. But each panel took less & less time.

Next thing will be adding a U2K to get the XM going.