grand cherokee infinity system problem

Hello All, I just purchased a used 1999 Grand Cherokee Laredo with the Infinity Sound system. The four front speakers all work fine, but the two in the doors in the back do not. I took out the factory head unit, bought a wiring harness from Crutchfield and used that to install an aftermarket radio (Alpine). Again, the front four speakers work fine but the back two do not. My brother had an extra Infinity amp, so we plugged that in - fronts still worked but backs did not. I went to the plug on the amp and checked the resistance for each speaker. The front ones were at 2.5 ohms each; neither of the back ones registered. I think that this means that the two back speakers are blown. Is that correct? Seems odd that (1) both are not working and (2) there is no noise coming from either - my experience has been that when a speaker blows, it'll rattle/hiss/etc. but usually not just quit. Is there something else I need to check or should I pull a door panel and check a speaker? Thanks in advance for any advice.

pull the panel, disconnect speaker, check resistance of speaker...if around 4 ohms, assume speaker maybe good.then check continuity of wiring from amp to speaker.

if the speakers dont register anything when tested with a multi meter then they are either completely blown or the wire is unhooked or broken somewhere down the line. it is also possible that this is the type of infinity system that uses a small amp on the back of the speaker, which means that you wont get a typical measurement when you test the wires with a meter. this is just a thought and its probably not the case.

Okay, thanks for the advice. I'll pull a door panel and check one of the speakers directly.