Alan,
I've got a
'BRAND NEW STILL IN THE BOX' American Auto-Wire waiting for me to get off my deadbutt and install it. Are you go'na shame me into being productive....?
Sure you can TEE off the brown wire....
If the BROWN WIRE feeds to the coil, then I would put the aforementioned diode between the TEE and the GREEN LIGHT. This will keep backflow from feeding the coil. But, if ya put the diode between the alternator and the Green Light, (and the diode is working properly), the GREEN LIGHT might not go out as it should not receive any positive power from that direction...! At least in theory.....
Danny