No ignition switched 12V feed to radio

[dme123]

I have been battling with the radio on my 1992 XJRS. At some point in the past someone has wired the switched and permanent 12V inputs to the radio to the permanent (radio memory) feed from the car. This has caused it to keep blowing fuses.

It turns out they have done this because there is no 12V feed from the ignition switched power to the radio (purple cable). Obviously I've checked the radio fuse (10 amp) and that's fine, but the wiring diagram shows some sort of odd arrangement with the drivers seated heat relay for the power feed to the radio. Any advice on how to resolve this would be gratefully received!