Thanks for all of the replies.
Chryco: do you happen to have a link or a part number for the micro switch you mentioned? Think it would mount to a Slapstick shifter?
Matt70: do you have a pic that you can post?
Katfish, WildR/T: my A-518 will use pressure sensors and relays to automatically shift into OD. But I want to have a master switch that I can throw to enable/disable the OD. My reason being that around town, I'll turn the OD off but before I get on the hwy, I'll turn it on.
djw383, burdar: not a bad idea, kind of like what gear vendors does. I'll definitely keep it in mind.
brads70: I actually thought about that a few days ago. I even looked at on old switch panel that I have. I'd either have to get a panel with openings for 4 switches or make another opening in my switch panel.