Hello my learned friends. I'm blessed with a beautiful 1997 Jaguar XK8 convertible. During the winter months it stays parked. Unless driven regularly the battery drains to the point when jump starting is the only solution. Recently I failed to keep the trickle charger connected.My fault. Surprisingly, the drain is sufficient to prevent starting after just 10 days.

Is there any easy way to troubleshoot the car's electrical system so I can discover what the electrical drain while it's parked.

Thank you in advance for any suggestions.

Very respectfully and cheers!

Bob G in Florida

 

Use a voltmeter across the battery terminals to determine available voltage with the ignition in the off position to eliminate the possibility of the battery being weak. There should be a minimum of 12.6 volts available for all modules to function properly.

Once the available battery voltage is confirmed, begin by disconnecting the negative battery terminal. Place the voltmeter between the battery terminal and the disconnected terminal to determine the mili-amps being drawn with the ignition off. If there is a draw of more than 40 to 50 milliamps, the battery can discharge within a few days.

If there is more than 50 milliamps being drawn, find the source of the parasitic draw. Begin unplugging fuses one at a time to see which circuit is causing the draw. Once the voltmeter indicates a drop in the draw, use the vehicle owner's manual to determine what components are powered by that circuit. Next, begin disconnecting the component plugs one at a time until the parasitic draw stops. Leave that component disconnected and reconnect the remaining components to see if the draw begins again. If it doesn't, you've identified the component causing the parasitic draw.

 

Good morning and thank you NBCat. I greatly appreciate your offered solution to isolating the parasitic battery drain. Had I stepped back from the problem, I would have realized the proper way to isolate the drain would be by removing fuses and powering circuits one at a time.Shame on me.

I do have a question. Please excuse my ignorance. With the battery negative cable disconnected, please say again where the voltmeter is applied. My understanding is from the positive battery terminal to where? With a fuse removed, my assumption is the open side of that fuse location, basically completing the voltage measurement one circuit at a time. A measured drop in voltage implies something on that circuit is alive and drawing current.No voltage measurement implies the circuit is completely off - example headlights.

I hope my wordy summary is correct. I'm basically using the voltmeter to complete a circuit from the positive battery to the load, one fuse location at a time. From there it should be easy.

Very respectfully, Bob G in Florida

 

The voltmeter is placed between the disconnected negative cable/lead and the negative battery terminal to complete the circuit.

 

My bad. Of course you're correct. I should have realized the answer. Thank you for your patience with me. Results to follow by next weekend.