Thanks for your prompt reply, nezarnuaimat. I think you are right: I need to get an experienced electrician to have a look at it.
By the way - have you connected the illumination cable on the back of the HU to a power source? In case you have, do you remember what source/cable?
And the same with the reverse camera (I have an original one), do you remember where to locate the power cable for the reverse lights?
Is there anything that can be connected to the cables of the original HU. Now I have just stuffed those cables aside inside the dashboard.

Thanks a bunch for sharing. Very much appreciated.

Yes, I remember my electrician found out that I did some wrong connections and he corrected them. I really don't remember well but he connected the PWR-ANT wire to a +12 VDC source (look for a red wire inside the harness), he added a noise filter plus a bunch of other items. You need to see an expert pal. Now my HU is working just perfect.

Make sure you take this photo with you. Its different brand but has similar connections

http://www.eonon.com/UserFiles/image/D5124-06.jpg

Good luck ;)

I know this is an really old stream.
My hualingan has been great, but recently the firmware has gone haywire.
Does anybody know where I can find a download for the HL-8786GB WINCE 5.0 firmware.
Thanks in advance

I didn't find an exact link to what your wanting but this is a good place to look :

https://forum.xda-developers.com/windows-mobile/general