Mercury 150 Manual page 70

BATTERY CABLE CONNECTIONS
Single Outboard
a - Red sleeve - positive (+)
b - Black sleeve - negative (–)
Dual Outboards
Connect a common ground cable (wire size same as engine battery cables) between negative (–)
terminals on starting batteries.
a - Red sleeve - positive (+)
b - Black sleeve - negative (–)
OUTBOARD INSTALLATION
b
(-)
b
(-)
c
a
c - Cranking battery
a
b
a
(-)
d
c - Ground cable
d - Cranking battery
64
(+)
c
or86
d
or87