I'll agree with RaOul and Big Al in so far as your voltage measurement with
all the accessories on at idle..... Unfortunately, I have seen many cases
where faulty diodies can show us a high charge voltage but leave us with
insufficient current to properly charge the battery. What we really need to
measure is alternator current output along with the voltage to determine if
the charging system is operating at full capacity. This should certainly be
enough to keep the battery charged unless we have added high current
acessories..... remembering that the factory built the vehicle with an
alternator sized for the vehicle in it's normal "dress".

Another useful measurement is alternator ripple - this can indicate bad
diodes. Turn your DVOM or DMM to AC volts..... connect the black lead to the
battery negative and the red lead to battery positive. Your reading should
be < 90mV.


> wrote in message news:TbJyd.573074$%k.417262@pd7tw2no...
>
>
> Hi;
>
> My 97 cobra is parked and my 86 2.3 LX winter beater is out!
>
> Background;
>
> With headlights, turn signal and heater/rear defrost on, the rate at which
> the turn signal flashes goes down significantly than when there are no
> accessories running. My assumption is that the electrical system is not
> producing enough juice at idle to power everything properly.
>
> With the car off, I am reading 12.1 volts at the battery with my Fluke
> multimeter. With the car at idle, and no accessories turned on, my
> multimeter reads 14.09 volts at the battery. HOWEVER, with all
> accessories on, and the car in drive (yes Jim W, parking brake on and
> someone in car with foot on brake ), my multimeter only shows around
> 12.5 volts at the battery.
>
> Question:
>
> Is 12.5 volts at the battery a normal voltage reading given all accesories
> running and the car in drive? The car seems to run fine enough, but I want
> to make sure I dont have electrical/charging problems over the winter.
>
> TIA,
>
> Chris
>