FH Version 3 central lock and night heater

FH500 V3, Central locking and night heater stopped working, tried every fuse and relay, they are connected on the fuses but none i can find are blown, switch lights up for night heater but does not fire up, any help please

Howardplant:
FH500 V3, Central locking and night heater stopped working, tried every fuse and relay, they are connected on the fuses but none i can find are blown, switch lights up for night heater but does not fire up, any help please

I have had this before, I seem to recall they’re linked by a black box that controls both of them, something to do with operating with the ignition off. It was a long time ago though so memory is a bit rusty. The cause was a direct short on the central locking motor.