Jaguar Repair: car repair, battery cables, simple tests

Question
My 87 jag xj6 The battery keeps going dead after i turn car off.

Answer
Hi Jamie,
To determine if something is running it down or it is just a bad battery you need to do a couple of simple tests. You need a volt meter and a 12v test light.
First check the battery voltage (12+v) Then start the engine and set it at a fast idle 1500 RPM and read the voltage across the battery posts (not the cable ends). (13.8 to 14.5 volts)
First question is do you have a high tech radio or disk player added to the car? Some new radios and disk players have a coded system that requires the code be put back in when a battery cable is disconnected. If so, you need that code before proceeding to the next test.
With EVERYTHING turned off, remove either one of the battery cables and put the 12v test light between the cable and the battery post. If the light lights up brightly, you have a draw that can run a battery down. If you get a bright light remove the wires off of the back of the alternator (no small job) However, this is a necessary test to see if the diode pack in the alternator is bleeding the battery down after shut down. If that don't put the test light out you need a wiring diagram and just start disconnecting one fuse at a time to try to isolate the draw to a smaller area. (a lot of work).
If the voltage tests were ok and you had no light or a very dim light on the 12v test light then you need to have the battery "load tested".
Howard