Thetford C200 CWE Cassette Toilet Function

When you say flush button, I assume your flush is electric so this may not apply to yours but on our manual flush C200 the light next to the flush push handle is operated as described above by a reed switch but also has a couple of batteries located in a holder in the left hand wall of the cassette compartment (either AA or AAA and it's too dark and wet for me to go out and check which at the moment!).

However I'm guessing if yours is electric flush they would also have designed the alarm light to work from the van 12V supply, but I don't know for sure.

Incidentally, I hardly ever bother fitting fresh batteries; it's fairly obvious when the cassette needs emptying as you can see the level when you open the flap.

The light works on ours, but as Paul says, it's very heavy by that stage.
Also the instructions that state '5 uses left once the light comes on' is a little ambiguous. The one time I saw the light come on it turned out there was only enough space for, er, half a use..
Al.