Diagnose
Each tree is a short conversation. Answer what you see. You will land on a fuse, a cylinder, a Hall sensor, or a battery.
Head unit dark, no sound, no display
Most ‘dead radio’ cars have a fuse, a trunk battery, or a Bose amp. Work top to bottom — do not pull the dash first.
Convertible top switch does nothing, or the sequence stalls
Split the job: silent switch is electrical. A pump that runs and a top that stops is hydraulics or a limit switch.
Central locking, IR remote, or fuel flap dead
Pneumatic, not electric. The dash button is the fork in the road.
Starter turns, engine does not fire
Split by generation: HFM/LH cars want spark, fuel and a living harness. ME cars want a crank sensor that still works hot.
Left or right glass will not move, or the roof aborts
A window that does not know where it is will also kill the convertible-top sequence.
Car is dead after a few days
PSE pumps that never sleep and trunk lamps that never go out are the usual thieves. Measure before you replace the battery twice.