Any tricks to get a stubborn halide to fire?

[Delphinus]

Thanks for the suggestions, guys.

The ballast that fires neither bulb did work a month ago. Now, it's possible that since then, the cord from the ballast to the socket somehow got fatally stepped on or kinked or something like that. I haven't been able to check the integrity of the wiring yet, but that's next. Other than that ... I don't really see how it could have failed. I suppose it could be the capacitor... hmmm. Can one readily buy a replacement capacitor for these things without the transformer? Seems to me at that point it's maybe easier to just buy a whole new ballast.

Basically I tried several different permutations. I swapped ballasts to the left and right sockets several times, I swapped bulbs left and right. I also swapped in my old Iwasaki bulb (about a year old ... it's a non-R version but it lights fine -- my 20g was once lit by this bulb). One ballast lights both the one "new good" bulb and my "old good" bulb, but never lights the "new bad" bulb. The other ballast doesn't light any of them.

I'm off to try a different set of wires from ballast to socket on the one errant ballast. I'll post back if I find anything new.