NOTE:This post from another site:-
Related Products：LAUNCH X431 HD Heavy Duty Truck Diagnostic Adapter
A converter with 30 to 12 volts or a battery. I disassembled the cargo ECU. There a bunch of converters from 24 to 12 volts and the standard CAN and KL chips are powered by 12 volts. And for KL you need to select a capacitor (taking into account the passenger cars 4700 pF) for freight you need somewhere 6800- 8000 pF. Ie additional 2000-2500 pf (between the K-line and ground) is a simple KL-adapter, but that's what the JV700 needs to look at. Concerning the "X431 HD Heavy Duty Box HD Adapter" (this is as an add-on) it can work on this program, but there must be another account for the PRO3 adapter. It's easier to buy a dolphin or a car.
from someone's post:-
Can. But you need a table then everything is equal. There is nothing complicated. A pulser, a suppressor of 14-15 volts. Optocoupler 4 pieces or 2 dual pair of resistors per 10k and a pair for 1k and two trunks approximately ... It is possible and without optocouplers on 4 trunks and to protect 2 more suppresses
new drawing from post
you can put a mini voltmeter to a heap.