For the wiring to the transfer case switch, see
https://www.ausjeepoffroad.com/forum...0&postcount=17
I soldered my new pigtail in from underneath the car. Most of it was done blind, but having poor near-field vision working by feel is a skill I have developed - as well as being pretty gun with a soldering iron. You can now get doohickies that are a combined heat-shrink-come-solder-joint which might make it easier. See
https://www.ebay.com.au/itm/374920406803
Based on your original problem, it
was pretty clear that you had the dreaded transfer case switch problem. I chased mine in circles for months before realising that the Dorman brand ones are incompatible with the WG. Replaced it with another brand and, presto, it all worked.
However, your newer issues appear far more sinister. You might do better to try to get a second-hand ECU and transfer the SKIM chip across as we discussed the the ECU thread. I have heard horror stories of people trying to get ECU's repaired.
To answer your real question; sorry I do not know anybody in Melbourne that does ECU repairs. That said, Robert Bosch Australia is based in Clayton. I'd contact them. You might get lucky.
EDIT:
P1608 could also be:
A to D Monitoring, RAM Test Failure
A to D Monitoring, Ground Connection to PPS Failure
A to D Monitoring, Test Voltage Failure
The diagnostics path for all these all rapidly end with "replace ECU" unfortunately.
Obvious question... have you cleared the errors to see if they come back? I would triple-check the ECU earth and the engine is well earthed.
Which wire would you like me to test for 5V? Let's do a step-by-step comparison, if you like. I am WFH tomorrow, so I can easily slip out back for 5 minutes to take a measurement, provided you pick something easy to get to and be specific.