Jaguar Repair Problems? Ask a Jaguar Repairs Expert.
Have you tested directly between the alternator positive post and engine ground? We're trying to determine if
1) the alternator is functioning
2) if we have a ground or wiring problem somewhere along the way.
What are you using to test for voltage?
I'm not quite sure what the dump valve is that he's referring to either, but vehicle electrical systems all have certain commonalities.
First point of order:
Get a multimeter, and hook one lead to the large terminal on the alternator, and one to a good engine ground. If you have a good 14.5v or so while running, then you've got yourself a ground problem between engine and chassis. If you don't, then it's possible that you have an engine wiring issue, but more likely that you have a faulty alternator.
Please check this, and let me know what you find.