What andy said ^^^^^

my 08my has the constant green trailer as it has the factory wiring kit. However i suspect that with a scotchlocked kit there will be a buzzer/sounder unit somewhere though with the amount of deadening in the car it may not be easily audiable. There is nothing that can't be fixed with a hammer😜😜
FFRR 4.4 SDV8 Autobiography Santorini Black.
Fiat 500x 1.4 multiair Lounge 2015
2010 LR D4 Commercial 2.7 TDV6

My 02 HSE has no warning lamps but if I remove a bulb from the trailer it comes up with a dash warning "Check trailer light". It does however lock the suspension. I have always assumed that because it recognises that the trailer lights are good or bad then this is enough to comply with legislation. The Best 4x4 by far, so long as you have deep pockets.