Hi, Lori.
We changed the ballast between vivs and the non-working one works and the working one doesn't.
This sounds like an electrical difference between the two vivs, rather than a problem with the ballast.
I'm sure you've tested the bulbs themselves, and both work in one viv but not the other...
And I'm sure you've tried putting a table lamp into the mains socket of the viv that "doesn't work" to check the fuse, the socket itself, the wiring, etc....
The ballast ignites the lamp with a powerful, high-voltage pulse and if anything (dirt, oxide, damp) causes a voltage drop, the lamp won't ignite. If neither ballast work in one viv but both work in the other - and so do both the bulbs - then I'd guess it could be a problem with the ignition pulse not reaching the lamp in the "problem" viv...
So the first thing I'd try would be to examine the pins on the ballast plug and the lamp plug - ie. the points where an electrical connection could be weakened. Have any of the wires come loose? Are any of the pins bent, dirty or coated with oxide? Sometimes I gently rub over my pins with fine sandpaper to freshen up the connections.
The next thing I'd definitely try is taking the bulb out of its fixture and doing the same little freshen-up operation with the base of the bulb, and also the inside of the lamp fixture... check the little pins inside the ceramic lampholder are sticking out as far as they should, and are shiny and clean. I have several different fixtures for doing my lamp tests, and often I have "failures" due to bad connections inside the lamp holder. Most can be fixed with very careful bending of the springy bit inside with my fingers, and fine sandpaper.
Is it a dome fixture, resting on top of a mesh lid, or is the lamp an integral part of the vivarium and, for example, wired through the ceiling? In both cases, I'd also check the wiring where it joins the fixture. Heat will make the outer plastic coating on the inner electrical wires go brittle with time, and sometimes these crack or come loose.
If none of these things work.... :silent:
Is there a different sort of timer on that socket, or is it supplying more than one appliance, or anything else that could affect the electricity going through?
Best wishes
Frances