Duh!
Well good news. I did an experiment using the train-line and the LEDs come on to full brightness as soon as I crack the throttle, before the loco moves! I was going to hide a battery pack in the load, but now I can save the hassle and just wire it to the train-line.
I’ll wire it up so the plow that is moving forward will be lit. Need to add the same array to my existing plow and put a train-line plug on the back of my trail car and we’ll be all set for night plowing. Interesting that when polarity is reversed they glow just a bit. Probably explains why I never get three toots in reverse.
Been taking pictures as I build the light arrays that will get posted tonight.

The hardest part was getting the train-line out of the rear of Cheesy Sound / Battery car. The connector I used was reversed polarity so I ended up doing it twice and of course when I took it apart the second time wires broke. But all fixed & functional now.