Originally Posted by BGTV8

With the headlights on, I reckon that the ECU "saw" power in the brake light circuit as it is bridged to tail light circuit and the ECU interprested this circumstance as "the brakes are being applied" - the ECU won't permit mnre than nominal sustained throttle opening when it thinks the brakes are applied ... it will let you "blip" the throttle ina heel/toe maneuvre but will not supply sustained throttle opening when it believes you have applied the brakes.