03 rear defrost

[ogre73]

Hello all, I am looking for some help on my rear defrost issue.
What I know:
There is no voltage being dropped across the heating grid from one tab to the other; I measure 0 volts.
There is no short to the radio antenna; I measured open resistance.
There is no problem with the relay that provides the 14.5 volts to the grid; I measure 14.5 volts with the grid disconnected.
There is a small black box, that Chevrolet calls a "module", behind the driver's side rear pillar. I have removed this, checked all connections, and put dielectric grease on the connections before I re-connected.

What I think:
Is that there is a high impedence connection or start of a break somewhere that is dropping the voltage across it, and that is why I am not seing the drop across the heating element.

What I haven't checked:
The wiring from front to rear, as it has been very cold, and that is hard to get at.
The circuit breaker, because I can't find it!
Help me here, please!
Here is the passenger side fuse/breaker panel: . You can see that it has the relay, and that is great. But this label shows the breaker as being here somewhere, and when I pull off the cover that is on the right there, all there is are wires coming from a connector.
I would like to find the breaker, and I would like any ideas that anyone has.
Thanks in advance.
Ogre

[ogre73]

bump. I could use some ideas, if you have any. Thanks.

[ogre73]

Update.

Symptoms appear to have changed in the last few days, and I am thinking that perhaps the battery has a lot to do with my problem.

I made it to the library earlier this week and managed to get a look at the GM manual for troubleshooting this circuit/problem. The book was extremely detailed, (had a wiring diagram for the rear defrost circuit by itself, for crying out loud) and I didn't have a lot of time, but I did gain this much from it: the BCM has a say in whether or not the rear defrost is allowed to operate. Apparently, the BCM evaluates the battery voltage to determine if it is sufficient to allow the rear defrost to take from it. Why is this signifigant to me?

We had been having an awful cold snap here in central/northern Maine, and the temperatures were well below freezing, with wind chill way below zero. My battery was sluggish turning the car over most mornings, and I think that it is starting to go anyway. As a car battery only has about 40% of it's available current at 0 degrees F, and only about 60% at 32 degrees, I don't think the BCM was seeing the voltage that it wanted to allow the rear defrost to operate properly.
Backing that up (I hope) is the fact that today, with the temp at about 35 degrees, I put the test light to the relay input - lit up. I turned on the rear defrost with everything connected and put the test light from ground tab to hot tab, and nothing for about 3 seconds. Then, I could hear the RPMs drop and a load on the engine, and the light flashed for about 1 second. RPMs increased, no load, no light for about 5 seconds. Then again for 1 second, then about 3-4 nothing, then flash again. You see where I'm going with this.

So I guess the next step will be to change the battery and see what happens. I need a new one anyway, so hey, if that fixes the rear defrost, too, then great! If not, then at least my symptoms have changed a bit and I have something new to go on.

I will keep this post updated on the progress.
Ogre