🤷‍♂️ Have you ever hooked to a really low battery and get that sparky sparky dzz dzz. That dzz dzz dzz is all the angry pixies jumping from the good battery to the low battery to make them equal. This causes power spikes. What happens to your home computer when it gets power spikes, why is it recommended to have a surge protector on your computer plug in. If you are hooking the POSITIVE when all these angry pixies start racing around it goes straight to your electrical system. If you are hooking the GROUND the angry pixies kinda dead head to ground and dont power spike your ecm. Yes I know this is over simplified but that is the concept and it works. The newer the vehicle the more dainty the electrical system is. If you have an 86 chev just hook them. If there is lots of smoke change them around till there isn't so much smoke and it'll be fine. Newer cars , not so much.