On May 21, 7:17*am, tem wrote:
I have 1986 Mercruiser 170 (mdl MCM 170) w/ 2 battery system. This may
be a dumb question, I'm not a mechanic. My volt meter reads 12.3 on each
battery when engine is not running and 12.2 after I started it. Does
this mean my charging system is not working? Any help or advice is
appreciated.

--
tem

There are a number of ways that could be wired but generally that
doesn't appear to be enough voltage to be charging.

Your basic 2 battery switch connects the system to one or the other or
both of the batteries. That includes both the alternator as well as
the rest of the rest of the 12v system. More advanced 2 battery
systems may have separate charging circuit that connect the alternator
to both batteries independently of the battery switch. They are a lot
less common than the basic setup.

You could try the system with the switch set on each battery alone and
check the voltages running and off. If you have the switch in the
both position a single bad battery could be causing misleading
readings. Right after starting the motor you should see around 13.8
volts.

The original charging system on these motors is a real nightmare. If
it is broken and has not been converted to a regular alternator you
might want to consider doing that. The initial investment is a few
hundred unless you are competent to fabricate your own brackets. But
after that you can use ordinary one wire marine alterators which you
can get all day for under a $100.