Gee, just like in post #3.
That box that looks like it was after market on the driver side fender under the AC hoses is the relay and fuse for the CHMSL. It is a separate circuit from the other brake lights.

 

Found the box. It only has a relay in it. I pulled the relay and bench tested it. Appears to be working. Will have to check for voltages later tonight when I have more time. 3 of the 4 bulbs ohm'd good. 1 is blown.

 

The cruise control won't work with only 3 bulbs. Does it work at all? Are you testing with engine running?

 

4 brand new bulbs and a new relay, just because. Nothing, nada. Just loaded the dogs up and took it for a drive. Cruise worked once and then would not engage any more. No 3rd light what so ever. All other lights are fully working. Is there a wiring diagram of the circuit I can download?

 

It doesn't tell much, just that fuse #9 on the BCM controls the CHMSL then the wire goes to the CHMSL, the TCM and the ECM (that is because the light controls the cruise control).
Here is a pdf.

exterior-lights.pdf

 

Fuse 9 is good. I already pulled and checked it. I first noticed it not working before I took it into the dealer. Figured it was just bad bulbs and I'd change them out myself and save the money. Wondering if its not related to the door locks going haywire some how. Both controlled by the BCM. I'll try and rule out cut or bad wires first and if the relay is getting powered. Seen some evidence of mice running around.

 

Look at the ground wire locations in the rear 1/4 panel area. Clean and tight?

 

As of right now the white wire to the coil in the relay is getting no power from the BCM. Full voltage on the Red/W wire. The little CHMSL diagram I found makes it look that there is another relay inside the BCM that powers the white wire. Position 31 from the diagram.

 

I hate to complain but the schematic PDF's on this forum usually lack sufficient resolution to read the fine print (which is virtually all of it, usually.) I wonder if this forum's server is compressing the files automatically.

 

I’ve enquired about that and mostly it’s the source of the photos.