Engine Grounds
Attach one side to the battery then the other to the engine. If the problem persists, try the engine to the firewall. Rinse repeat until you find it.
If need be, You can use more than one jumper cable at a time.
I always run a 00 gauge ground cable from the neg battery post directly to the engine block and then from the engine block to the frame/subframe.
.
2 gauge copper seems plenty adequate for any gasoline engine.
It's the factory crimped ENDS of the wires that get " Resistive" with time and corrosion.









