I have managed to do some more work of the electrics, fixing the flasher relay, headlight relay, reversing lights, rear number plate light, and rear fog lamp.
I have replaced the original flasher relay with a LED compatible one from Classic Car LEDs LTD. Although I went through a number of fuses installing it, it now seems to work perfectly, albeit the hazard switch is no longer working properly… Two steps forwards, one back, and all that…
I have also installed an IVA compatible rear fog light module, splicing it into the old wiring harness. The installation was pretty straightforward and now means that the fog lights will turn off automatically, when you turn the car or headlights off, and cannot go on again until the lights are turned on again.