"Harry Bloomfield" wrote:

Remember the old type charge / discharge ammeters, where used a couple of
turns of cable which used to sometime be fitted to vehicles ? I have one
fitted to the tractor mower which is not marked + and - and I'm sure it
reads the wrong way. The needle goes left when on charge, I seem to
remember the norm is to move to the right.

Can anyone remember, before I take steps to correct it?

The usual orientation for a charge/discharge ammeter is with the quiescent
needle pointer resting at 12 O'clock (needle pivot at 6 O'clock); the
negative (-) discharge sector to the left (anticlockwise) and the positive
(+) charging sector to the right (clockwise).

Some ammeters (like yours) rather unhelpfully are not marked + and -.
However, they are usually colour-coded (blue or green sector for charging;
red sector for discharging), or annotated 'Charge' and 'Discharge' or simply
'C' and 'D'. Doesn't your ammeter have any of these legends or markings?

There are some versions of these ammeters designed to be mounted the other
way up, with the quiescent needle pointer resting at 6 O'clock. If your
ammeter is actually mounted upside-down (as has already been suggested),
then the needle would appear to read the wrong way. However, there must be
some lettering on your ammeter ('Amps' or 'A', or the manufacturer's name)
that would be inverted if the ammeter has been mounted the wrong way up.

When you say, "The needle goes left when on charge...", is that when
charging from an external battery charger, or when charging from an engine
mounted alternator? If the latter, then your alternator could be faulty and
not generating enough output to meet demand.

Check the wiring diagram (if you have one!) to see where in the circuit the
ammeter has been located. Also check the ammeter connections to see if it
has been connected reverse polarity.
--
Interloper