FORD 2003 E-550 v.1 - Manual (Page 186)

2. Reconnect the primary battery
ground cable.
Diesel engines
Disconnect:
Secondary positive cable remains energized after disconnection.
Make sure the tool does not contact any ground surface.
1. Disconnect the secondary positive
cable from the primary battery
terminal.
2. Wrap the secondary positive cable
with a non-conductive material to
insulate.
Maintenance and Specifications
186