OK, so I'm getting an error msg on dash "check rear lights, cruise control disabled". I chk and find the 3rd brake light does not light with the other brake lights. Calling all my parts sources, OEM and breakers, throughout the country and CDN to find it is obsolete! So, here's my question... can I erase the yellow msg since the other brake lights work and drive while figuring out an alterative to replace the 3rd light?

 

have you checked the high mount stop lamp fuse, on my MY at least it is fused separately.

 

YES

 

My understanding of the 3rd brake light is that it's not part of the canbus system, so unlikely to be your error msg.
More likely it's your brake peddle switch.

 

Doubt the brake pedal switch since the main brake lights all work properly.

 

^^
H-M lamp is not monitored for fail, but the same circuit (post-F8) flags back to the ECM that the brake pedal has been pressed. That may be the reason for the check rear lamps message (IDK for sure) , it may be the brake switch as noted, or wiring in between.

Do you have B+ on both sides of F8 (ignition (ii) and brake pedal pressed)?

 

Pedal switch is two switches combined:- one N/O closes when pedal pressed (brake). one N/C that does the opposite (cruise cancel):- or that's what should happen. Both switch states are inputs to the ECM.