Right then,fair play for you,to do the further fiddling
As i alluded to,the electrics on them Kugas,can be "challenging".
I am flying blind,here,but your vehicle may have the electric boost,for the heating circuit.
This is to aid rapid demisting,from cold,and is usually nothing more than 4 or more glowplugs,in a heat-sink,through which the heater water flows.
It uses plenty of amps,as does the fan blower motor,on high,which is why these things have "load shedding",on the alternator output.
This allocates varying circuits,as if all the electrical consuming devices are on at once,it's melt-down. It can be anyway,as the 200A alternators,struggle to dump the heat...
Anywho...it sounds like it is a possibility,that the circuit your camera/monitor,is on,may be over-voltage,after all other current drawing items,have done their thing,and this may cause the interference.
Switching on the boost,will draw a sufficient amount of current,to maybe drop the voltage again,to a satisfactory level.
Some of these systems can and do,run at 16V+.
Another reason,could be the extra load,causes the load shedding,of an unknown current drawing item,which is the interference generator,and this is why it works.
Measuring voltage at the battery,will not always identify the problem.
I wish you lived next door,my friend,because whether it's a new 200 tonne piece of plant,or an Austin from the 1930's...i live for finding these little foibles i think i wasted my enthusiasm on stuff like this,through my life...instead of investing it,like my pals,on ---- and beer
As i alluded to,the electrics on them Kugas,can be "challenging".
I am flying blind,here,but your vehicle may have the electric boost,for the heating circuit.
This is to aid rapid demisting,from cold,and is usually nothing more than 4 or more glowplugs,in a heat-sink,through which the heater water flows.
It uses plenty of amps,as does the fan blower motor,on high,which is why these things have "load shedding",on the alternator output.
This allocates varying circuits,as if all the electrical consuming devices are on at once,it's melt-down. It can be anyway,as the 200A alternators,struggle to dump the heat...
Anywho...it sounds like it is a possibility,that the circuit your camera/monitor,is on,may be over-voltage,after all other current drawing items,have done their thing,and this may cause the interference.
Switching on the boost,will draw a sufficient amount of current,to maybe drop the voltage again,to a satisfactory level.
Some of these systems can and do,run at 16V+.
Another reason,could be the extra load,causes the load shedding,of an unknown current drawing item,which is the interference generator,and this is why it works.
Measuring voltage at the battery,will not always identify the problem.
I wish you lived next door,my friend,because whether it's a new 200 tonne piece of plant,or an Austin from the 1930's...i live for finding these little foibles
i think i wasted my enthusiasm on stuff like this,through my life...instead of investing it,like my pals,on ---- and beer 
