RTN is generally tamper return. TRG is trigger the former is a continuation of the negative feed through the bell tamper back to the control panel. The latter is usually a switched negative fed from the control panel which activates the bell. More info is required for a definitive answer e.g make and model of bell and control panel
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local