In reply to a message from king tut sent Fri 16 Oct 2009:
I think you MUST immediately invest in a meter that works. It is
simply not possible that the quiescent draw on an XJ40 is 2 mA. It
is around 50 mA on mine and that is fine unless you don’t drive the
car for weeks or the battery is NBG. When I had this problem, I
found that it was a shard of metal loose in the driver’s window
switch unit that was powering up the window even when it was
closed. There is a feed there for winding up the window even when
ignition is off (normally by turning the locking key while locking
the vehicle). The current draw was 11 amps when the window was
closed, not enough to blow the 20 amp fuse but certainly enough to
flatten the battery. I made a test rig by taking a low value blade
fuse and deliberately fusing it, then grinding down the side of the
plastic and soldering on two leads which I connected to an ammeter.
I then substituted this blade fuse for each fuse in the 3 boxes in
turn, and the very first one I tried (Fuse No 1, driver’s side) was
the culprit. I tested all the others just in case. By the way, I
did all this AFTER I had unecessarily replaced a perfectly good
battery and noticed a big spark on connecting the new one. A small
spark is normal as the various micropocessor power supply
capacitors charge up. Incidentally, I do NOT recommend using a
master switch and disconnecting the battery overnight. a) it can
work loose while travelling (dangerous) and b) you have to
reprogram the security on the radio each time you reconnect the
battery. Neither do I think measuring with an ammeter in the
battery lead is a good idea. Too easy to forget and key the
starter, whereupon several hundred amps flow and the meter and
leads are destroyed, possibly even causing the leads to catch fire.
Been there and done it all… Even to the extent of laboriously
removing the winder motor from the car and stripping the gearbox to
see if it was seized, then to laboriously and knuckle-grazingly fit
it all back in again, when I could have easily tested the motor in
situ by connecting battery to the black PM4 plug (each way round in
turn)!–
Alan (XJ40 3.6L 1987/8)
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