The thing here is once you hook the cables up, let the running vehicle charge the batteries a couple minutes before you even try to start the diesel.

With cheapy cables, you may have to let it charge for 15 minutes or more before you try.

That little alternator and little battery in a car take a bit to charge 1700 CCA worth of batteries and then cycle glow plugs drawing 200 amps and a 300 amp starter.

Notice glow plugs and starter add up to more than most car batteries have as cranking amps.