Since I bought my 03 XJR with 59K miles in Aug, I have had false alarms, on-off interior lighting while driving, lack of a useable car alarm, no puddle lighting, false door-open warnings on the cluster, and no interior lighting when I actually need it (gathering my things while exiting the car at night).
I've researched the sensors and their sizes (found none). I've taken the latches out of my doors for hopes of rehabilitating the sensors but found heavily corroded switches that fell apart in my hand. These fragments have been rattling around causing the on-off conditions. The sensors alone are not avalable from the dealer. Complete latch assemblies cost around $400 apiece. Salvage yards such as Coventry West and Jag Graveyard have used latches starting at $150. I need three.
I finally found a seller on eBay breaking his 98 VDP who was asking $90 per complete latch. They looked very clean. I offered $225 for three (shipped) and he took it. I feel this is the best I can do.
The lingering question is why are these door sensors exposed to the elements and what can I do to prevent it from happening again? For clarity, this is not a flood car and has not suffered any other electrical problems.

 

One of these should fit...
Saia-Burgess - Switches
(Link is stolen from a thread here, but I can't find it, sorry.)