The wiring usually suggested is positive to positive, and live negative to bare metal on the dead car. Th negative terminal is supposed to be connected to this metal, so you are still making a complete circuit (using the car as a bit of wiring)
You can just connect negative to negative and it will work. The idea behind connecting to car instead of battery is that the battery can create and release hydrogen gas while charging (particularly if it is damaged). Disconnecting a wire from a live circuit can create a spark; connecting negative to car means the potential spark and the potential hydrogen gas are not at the same place.
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