Well that changes things, this vehicle is listed as possibly having daytime running lights, so the brake lights don't work at all when you turn the switch on fully to headlights, or does this happen when you turn the switch to the first Park lamps, and any change with high beams or low beams?
And the rear Turn signals, Park lamps, and Brake lamps all share the same Ground wire, are any of those affected by the head lamps being on?
The Body Control module controls the head lamp relays (both high and low beam) as well as the Park lamp relay.
The Body Control module takes an input from the Multifunction switch which controls the head lamps, park lamps, etc.
It's possible there is something going when the Park lamps are turned on that's effecting the Brake lamp bulbs since they both use the same Ground in the rear of the vehicle, so it may not be just the head lamps being on, The Brake lamps are not controlled by a relay, the power is applied through the brake switch on the pedal to the Brake Lamp bulbs so it may be that the circuit may not be able to carry enough current flow due to a possible bad ground or corroded connection somewhere going to the rear lighting assemblies.
So, check if the issue happens when just the Park lamps are on.
It's difficult to give a definite answer as to what the fault is, but the Ground and the Park lamps might be part of what's happening, when wires can't carry enough current flow due to bad connections, current will flow on the easiest path available and to whatever bulb circuit has the lowest resistance.
Wednesday, February 5th, 2025 AT 2:16 PM