My camshaft sensor light is on. and how u know when u need to change catalyic converter

Nice anon double post.
so there is no camshaft sensor light on,! (typo?)
why not post a photo of that so we can all laugh.
my guess is its a typo, you meant my check engine light is on.
that? RUNNING? and does it run, ok, (other shoe drops)

yes, that means to scan the pCM
the CAT is bad if the PCM tells you its bad. (p042x) means its bad.
(the smog station will fail it for that. or CEL on running)

or if the engine wont start and CAT melted closed, and the back pressure to it is over 2psi. (easy test)
or the vacuum test fails, cranking or idling if it starts at all.
if the vacuum is near zero cranking ,ONE cause is melted cat.
easy tests all, but is guessing....(BAD THAT)
why not post The full symptoms, not just easter egg hunts...and such.
AND NOT post anon, so we can see you do many posts and form full ideas of all problems posted, (continuity of facts)

WJ 03 jeep
what light , again, here is your cluster, what lamp again?????
that lamp is CEL, not Cam. (apples and oranges diffr)
(aka, MIL & SES) See icon is engine shaped?

or did you scan the PCM (good idea for sure)
did you get P03xx errors (called DTC's) and the book says
cam?
please say what object showed you CAM?
we cant guess that. say it please.....

Replace cam sensor if all wiring looks ok. For cat converter, vacuum gauge can be used to test for restricted exhaust. O2 sensors normally have one upstream of converter and one downstream to check for proper operation, so you should get a check engine light if the downstream O2 sees a problem. You may also notice a smell of rotten eggs as converter goes bad, and when really plugged up they can get unusually hot or even glow cherry red!