Interesting dc/dc issue

Hi ya'll,

First, Im new here but not with G1, G2 Prii, I have 6 in the stable. I collect, repair, rebuild G1 and G2s. I pulling a G2 off the back burner with an interesting issue on the 12v side of things. First some history.... This car was in daily service, 150k ish miles, no issues, no faults, good batteries etc.... One day I noticed a faint high pitched singing from under the hood and at the same time my normal 14.x volts dropped to 11.x. No codes or faults. Open inverter tank and coolant is flowing nicely but finger test indicates way too hot. Hot coffee too hot. This could have been going on for months as Im not the primary driver of this car. Again keep in mind, no codes, faults or lights, good 12v and hv batteries. So having no time at the time and plenty of spares it was parked. 5 years later (last week), I connected a new 12v battery and it started right up. About 2 minutes later, the whine started and the 12v battery sagged to 11 volts. So the problem did not fix itself over time. One authority i trust mentioned a connection on the transaxle, but outside of the parking paul, i dont that small wire could handle the current. Something is loading the dc/dc to its max output but not burning or causing codes or faults.

So what do you think?