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What's Killing My Battery?

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satzman

Jedi Hopeful
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A perfectly good battery was dead after only one week. After charging it, I had a disconenct switch installed. With the ignition off, I turned on the disconnect switch and heard some clicking towards the back of the engine bay. Something is connecting without the ignition switched on and apparently draining the battery if left unattended. Someone suggested that it could be a bad relay. Any thoughts?
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The only way to deal with this is to hook up a 10 amp ammeter in line from the battery and then begin to disconnect the various electrical circuits to isolate the problem. This should prove very simple since the Etype is a very straitforward automobile electrically with few electrical accessories. The normal drain on the battery with the ignition switched off is about .030 amps. Many times the culprit on a car as simple as the E type is in the charging componenets. Check drain in the alternator/voltage regulator/generator componenets. With the ignition off you should measure virtually no current to these components.
 
FWIW: in a "pinch" (ie: no ammeter handy) a 12V test light and good ol' "circuit isolation" -- pullin' fuses one at a time 'till the light goes out -- works almost as well.

Just suggesting an alternative.
 
I am having the same problem with the battery on my 1994 xjs convertible ,I`m looking for the reason why it is discharging when its just sleeping . I have just been advised to test each fuse to see if power is there when it should be dead this would then indicate a problem with that circuit.
terry1975
TR6 1975
xjs 1994 6 cylinder convertible
 
There are two things that I suggest. I have a 90 XJS V-12 conv. and had a similar problem.

Remove the black plastic cover over the relays just behind and above the battery. There are two relays for the fuel pump located there. Pull the red diagonal stripe relay and see if the problem continues overnight or over the period that the car "sleeps". I ended up installing an additional relay because I was getting some type of electrical bleed through that relay that was slowly motoring over the fuel pump. You can confirm if this is the problem by using mechanics stethascope and placing the rod against the fuel pump. I am not sure if the fuel pump was relocated into the fuel tank by the 94 model year or not. On the 90 it is mounted under the battery.

If it turns out that you can still hear a low growl from the fuel pump with the ignition off, I will tell you how to install this additional relay that opens the wire causing the problem when the ignition is off. It took me months to find this problem. My battery was going dead overnight. I installed a relay to open that wire and the problem stopped.

The other thing to try is to pull the fuse for the power antenna . Removing the relay won't solve it. The short is somewhere "upstream" of the antenna.

A friend with a 92 six cylinder coupe found that their short was in the trailer wiring circuit. They pulled the fuse and the problem stopped. For their 92, something besides the antenna was on that circuit. You can determine which fuse to pull from the fuse chart in the owner's manual. On the 90, the antenna is on the same circuit as the trailer "caravan" wiring.

See if either of those is your source.
 
What I recommend is to do the ammeter and fuse pulling drill to isolate the battery drain to the specific circuit. Then go into that circuit, find the drain culprit and replace it with a new or known good componenet. Don't add a "patch" to the fault to eliminate the drain. The Jaguar with the addition of electronic fuel injection is complicated enough! Think about the next repair when someone encounters an undocumented relay and tries to make sense of that. My apology Michael but it is one of my pet peeves when I encounter that kind of previous work. Jack
 
I know you guys are aware of this but every time I have experienced a battery drain it was the rectifiers (diodes) at the alternator. An inline test to each one should yield current in only one direction. This test is in the manual rather well explained.
 
I'm bringing the car to my mechanic in two weeks. The car is now in storage for the season. Thanks for asking.
 
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