In fact all 6 burned out!
I blame the bad connection in the makeshift plug. The wires just wouldn't solder onto the tabs, they gripped it by shape - but not enough.
So it had not been making contact for a while. I depleted the battery in EV mode, drawing its voltage way below the buddy pack - enough to make it bridge the bad connection and suddenly deliver the full voltage differential to the lamps.
I redid the tabs with a 120 Watt heavy duty soldering iron (the same I needed for the 6 mm diameter wires in the pack - a 30 Watt iron is helpless with those) and now the tabs are soldered through.
Also I swapped the lights round so the reflectors face the full open side:
It is starting to look like something that belongs on the front grill
Yet I'd rather not have that high voltage cable run the length of my car for a vanity show
__________________
2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut.
lifetime FE over 0.2 Gmeter or 0.13 Mmile.
For confirmation go to people just like you.
For education go to people unlike yourself.