Panel dimming

The pull-down DIM output of the HDX can sink a maximum of 120mA

If this DIM output is used to control the brightness of the intercom and the compass light, the current budget is as follows:

The Precision PAI700 direct reading compass has a built in light (incandescent)

Stated current draw of the lamp is 65mA. The measured (the lamp unit is marked 14V) current draw 125mA

The SV-INTERCOM-2S DIM input functionality is

It is pretty clear that this input most probably connects to a series LED/resistor tied to the positive rail.

The measured current flowing to GND with the intercom powered up and LED energized is 9mA

Without further buffering it is not practical to drive the compass light directly from the DIM output. Instead I am going to couple the compass light to the overhead light system.

I will - in the connectorisation - make both the input to the PWM dimmer and the the output available at the connector, so that the compass can be connected to either. The input to the dimmer will be it own CB managed "interior lighting" circuit. The dimmer output will be the "pos" input to the interior overhead lighting circuit.