If you have removed the fridge from the interior, set it up outside having first cleaned the burn chamber , nozzle, blown compressed air thru the air intake and flue,then ran it on a full 5 gallon portable tank with new two-stage regulator on a work bench , and it starts every time,  the obvious conclusion is the vehicles propane tank, regulator or copper pipes are defective.The fridge is designed to run on it's own, without help of running on AC first. 

 
    
I am struggling with this fridge.  
Connected to the car’s propane tank,
took it apart,
got it lighted every time first time,
put it back together,
lighted again first time every time,
installed the fridge into it’s place,
connected all,
it lighted fine,
put the outside parts on,
lighted fine every time,
put all the other things back on,
lighted fine, 
let it rest for hours,
Lighted, but while counting the seconds to keep the light on, it faded and stopped the flame.
repeated tries would not let it light up again.  
I have even connected the electronic tester with it’s millivolts to see if it starts at all.  But no.

Who can tell what to do?

My respect to this Great List.
Zoltan