At the recommendation of Stan2004 I bought a couple Azatrax MRAPR-12v DPDT 8A relays to control lighting for a couple 3 over 3 vertical MTH signals at each end of the block. They work perfectly. Now I am a little more daring and wondering if there is a way to wire up these particular relays where the signals are dark unless there is a train in the block? My current set-up is the following schematic:
Based on your description I would suggest simply disconnecting the green lamp. This will leave only the red, which will illuminate when a train is in the block. It will be dark when not.
Now, if you're trying to emulate what's called, in the real world, an "Approach Lit" signal it would be a little bit different. You would then need the same setup for the block preceding the one you have pictured above, without lamps. As soon as an oncoming train enters this preceding block it would signal the following block to activate whichever lamp is appropriate, red or green, depending on whether there is a train present in it or not, by switching on the power to the circuit in your diagram.
Try this for a flicker-free experience:
Try this, but the illuminated lamp may may flicker as an approaching train enters the preceding block:
Mike
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