Batboard

Batlabs.com wrote:Remote Speaker Audio (Pins 1 & 6)
An external four-ohm speaker may be connected
to the charger/amplifier via pin 1 (audio) and
pin 6 (ground return) of the plug, to provide both
remote speaker audio and internal speaker audio
at the same time.

Relay Dry Contact Closure (Pins 2 & 3)
When the accessory relay is energized, its contacts
close and present a short across pins 2 and 3 of the
connector. The relay contacts are rated for 10 watts,
maximum at 28 volts dc/ac rms. Within the limits of
the 10 watt rating, the closed contacts will handle up
to 750 milliamperes continuously and will switch up to
400 milliamperes of current.

Relay Closure Timing Control (Pins 4 & 5)
Pins 4 and 5 of the accessory connector are used to
select the time duration of the relay contact closure.
If these two pins are NOT used (open circuit), the relay
will remain energized for approximately 10 seconds after
an alert is received. If pins 4 & 5 are SHORTED, the relay
will remain energized until the 'RESET' button on the front
of the charger/amplifier is depressed. Pressing the
'RESET' button causes the contacts to open and turns off
the ALERT indicator."