the cables you made are not good for diesel startup duty at that length, They are good for civic and corolla only - that too for quick 2 second bursts.
The cables you want are 35 or 50sq mm size (1 or 2 awg) - the conductor will be about the size of your little finger, And the clamps you bought are very bad too, - they are steel and have poor surface area, better idea would be to buy 4 vise grips (grip plaas for you) and make them as ends.
Find proper cables, - for reference, the cable should be a little thicker than the one that goes across the radiator joining both batteries together.
The terminals are useless too - I know I could find proper ones in Karachi plaza market - they were used for marine use and standby generators, solid copper but tinned and extremely heavy duty - some were folding crimp type that required a 5 or 8 ton press or a stud type which requires lugs and nuts.
