Jaguar Repair: 1985 xj6 overvoltage reading, voltage gauge, regulator problem

Question
When the car is running the battery voltage gauge reads in the high red zone, (about 18v). With the engine shut off the battery voltage reads normal. Is this a problem with the alternator?

Answer
Hi Martin,
This is easy to test. Just put your volt meter across the battery and read battery voltage (12.5+). Then have someone start the engine and set the RPM at about 1500 and read the voltage. If you see over 14.5 volts, you do have an alternator/regulator problem.

Also check to see that you have the charge light on when you turn the key to just Ignition (not started). It would also pay you to check all major connections (+) and (-) and maybe even do "Voltage Drop Tests" of (+) and (-) cables.

Howard