Ford 2003 Explorer Owner's Manual page 203

Roadside Emergencies
Do not use fuel lines, engine rocker covers or the intake manifold as
grounding points.
Do not connect the end of the second cable to the negative (-)
terminal of the battery to be jumped. A spark may cause an
explosion of the gases that surround the battery.
4.0L Engine
202
2003 Explorer (exp)
Owners Guide (post-2002-fmt)
USA English (fus)