Dumb Question of the day, you can help!

[Jeff6.0]

I bought a used 1999 Tahoe a few weeks ago. As far as I know everything is factory original with the setup.
The rear speaker worked when I bought it but the both have stopped working.
Both rear speakers sound tinny, like there out of phase or something and have almost no volume.
Both front speakers sound fine.
I'm pretty good with home audio but don't know much about car audio.

Any ideas what's up?

How should I trouble shoot?

[RednckChevy]

just buy new speakers

[Jeff6.0]

I was kinda wondering if they popped. If so, they went out at the same time and that strikes me as a little odd.

[01xtreme]

Those radios are really easy to get out, I would pull the radio and check the resistance of the speakers. It sounds like they're on their way out, but it wouldn't hurt to check. (speakers should read something close to 4ohms)

[Jeff6.0]

Thanks. That's sounds like an easy thing to check. I'm on it.

[Jeff6.0]

Well, I'm getting 4 ohms across the Brownish pair and across the green pair. I amusing those are my properly functioning front speakers.

Across the blue pair I'm getting 5.4 Ohms and the pair next it on the jack (Black and mustard yellow) are completely open.
I'm thinking these two pairs might be my rear speaker but it's just a guess because I'm not getting 4 Ohms.

Can some one confirm the wire colors?

The speaker may have sung there swan song...

EDIT: Found a typical wiring diagram, I tested the correct wires.