Howdy,

if you are talking about mounting an ammeter in your dash to keep an eye on the charging system it needs to go in series with all of the cars electrical load except for the starter motor.

This can get quite messy as the ammeter can have upto 80 amps flowing through it and the cabelling needs to be large enough to cope.

for example: average car,

headlights 100 watts each
tail lights 15 watts each
brake lights 21 watts each
ignition (no injection or electronics) 50 watts
windscreen wipers, demisters, heater fan upto 200 watts.

so total watts used = 522 watts

Amps = watts / volts

522 / 12 = 43.5 amps

this is before you have added that "sick" CD player and amp (coupe of hundred more watts) and driving lights (200 more watts)
now we equal 922 watts =76 amps

Your best and safest bet is to use a volt meter instead. it is wired from any switched positive to ground and does not carry any load.
if the voltage is over 12 volts (13.8 is perfect) the battery is charging and if it is below 12 volts it is being discharged and will go flat sooner or later.

hope this helps.

Cheers,

Geoff