I was trying to keep from writing a book.
Yes, I did let the power supply alone run the car. Same deal, too heavy a load to not max out the power supply, 6.8V and 6A, then toggled from that to, 14.2V about 5 mA, about every 2 minutes.
But good point. It is a strong about 2 yr old Interstate Battery, clean contacts, and all cells in the normal zone, electrolyte-wise. This problem happened very suddenly. Something is drawing I’m guessing over 10A, when it happens, cycling 50/50 on-off time at about 2 minutes each state.