When lights are turned on ammeter drops to about 12 volts and gets lower if i run heater or wipers. What can be done to remedy this?

FYI the gauge is actually a volt meter. An ammeter is different.

If this voltage reading ocurs only at idle, this is acceptable. The volt meter should rise to about 13-14 volts as soon as you rev the engine, regardless of the number of accessories that are switched on.

If this is not happening, get a good volt meter tool and test the battery volts when the engine is running under the same conditions. Dashboard gauges can sometimes be inaccurate and not show a true reading.

The battery should show 12 volts when the engine is not running, and, when running, 13.5 to 14.5 volts.

Again, at idle with accessories on, the volts may drop a bit, but should rise to those numbers when you rev the engine a bit. If this is not happening, have a mechanic test the alternator for output and to see if the belt is slipping. A new alternator may be required.