The Gaffrig gauges that have the built in warning lights....Did these have a feature that triggered a warning alarm built into them, or did you need separate sender switches to trigger the alarm?

Same senders,light feature is build into the gauge

I guess what i am asking is, to hook up a warning buzzer, is there a terminal on the gauge that will trip the buzzer in the event of a high water, oil temp or low oil psi.

No, the red light is based on the guage reading and there is no terminal to wire an alarm off the guage.

If your looking got a way to trip a buzzar use a coolent fan switch that goes into a coolent passage off of a older fwd car,they trigger around 220 deg, they also make a low oil pressure switch that goes off around 5lbs..