@SteveH posted:It's possible you may not be connecting the negative lead from the power supply to the correct negative battery terminal.
The batteries would normally be connected in series (electrically daisy chained positive end to negative end from one battery to the next) when installed in the holder. If connections are made in the middle of a broken chain, the electricity won't flow to the LEDs.
I would suggest checking connections as follows:
The terminal marked positive should be correct. Only one of the two marked negative will work.
I believe you're pointing to the wrong place; with batteries installed, I suspect you'd read only *3 volts* across two of the batteries between the "plus" and either of the "minuses", and with the batteries removed, you'd read an open circuit across both.
Typically IME, one of the wires to the lights (through the switch, etc.) would be connected to, say, the contact at the bottom of the left-most battery where you've marked "-" in your annotation, while the other wire would be connected to the contact at the end *opposite* your "-" mark, at the top of the right-most battery. I'm assuming there's a metal bridge at the top between the left-most and the center batteries, and a similar bridge between the bottom of the center and right-most batteries -- other configurations are of course possible, but not common IME. Again, the frosted case makes it hard to make out the wiring, but closer inspection (or some experimentation) should provide clarification.
