I've done it before with one of these old 4-line shoebox KSU's where you can rewire it in a way so that when a call comes in and triggers the KSU to ring the phones (flash the lamp, buzz the buzzers etc) that it opens a circuit as long as it's ringing (and closes again when the line is answered or calling party hangs up from no answer) that can be used as a low voltage relay. I used this function to control a light in a radio studio that would come on while the phone was ringing using the KSU to open and close the 24v circuit to the light. (I'm not 100% sure as it was almost 10 years ago since I did that wiring job but it may have also involved moving jumpers around on the line card.) I need to replicate this function on a different system to hold a circuit open to control an external system while the line is ringing.

Does anyone have an idea of what I'm talking about and how I can do it again as I forgot the steps.

Thanks in advance!

Last edited by Rupert; 13 hours ago.