where can I get the Eberspacher Edith software and diagnostic lead so I can diagnose my D5WSC please?

Eberspacher Edith and software is no longer supplied and supported by Eberspacher.

If you require diagnostic kit for a D5WSC we would now recommend as below

https://www.butlertechnik.com/item/Eberspacher/heater-Basic-diagnostic-test-unit-221545890000/54Q

https://www.butlertechnik.com/item/Eberspacher/diagnostic-cable-Hydronic-water-heater-221000316300/54F

if you only wish to diagnose your own heater it maybe more cost effective just to upgrade your existing controller to an Easy Start T perhaps? Especially as we have them on a clearance offer currently - see link

https://www.butlertechnik.com/item/Eberspacher/Easy-Start-T-7-Day-Timer-with-diagnostic-12v-24v-221000328800/54L

Let me know