Thanks for the info. Small (important?) corrections and additional
info follows:

Seven bulbs in paralled and are 25 watts, not 40 watts. Resulting in
a total of 175 watts on a 300 watt transformer. However, one bulb
still burns at regular brightness.

The copper wire is 12 guage and stranded. About 30 feet long.

I though the low voltage yard lights were transformed to 12 volt DC
not 12 volt AC. Is that the issue?

Tom