Product Details:
Swann 42 Series push-on / push-off maintained pushbutton switch. SPDT - break before make. 250v AC, 10 amp. 12v blue illuminated pushbutton. 1.45"H x 2.69"L x 0.57"W. Fits 0.46"D hole. 1/4" "QC" spade terminals.

This is a unique pushbutton switch. The manufacturer has a pilot lamp, that illuminates the colored button, that is wired to common and N.O. Contacts. The pilot lamp is 12v DC. The contact is break before make. If you operate a 12v DC multi-pole relay with the NC contact, and use one set of contacts in series with the pilot lamp terminals and a 12v DC source, the lamp will illuminate the button in one position. Then when you change the switch position, because there is a moment between poles when both contacts are open, the pilot voltage does not short. By utilizing the opposite contacts on the relay, you essentially have a maintained switch the will illuminate when on, and go dark when off.