So I have two XJS convertibles, one '94 and a '95 built just a few months apart. They are basically twins, both being Flemenco Red. Interestingly they both suffer from the same type of problem. They draw about a 1/2 amp of current just sitting. On the '95 I pulled all of the fuses, I think there were about 40 total and none of them stopped the draw. On the '94 I removed the cables to the bus bar at the firewall along with the wires at the spur below the battery and still had the same draw on that one.
The question is, without these cables being connected what other hot connections are there? Is there another terminal post that I am missing besides the two at the firewall? I must be missing some other main power distribution connection somewhere. Any ideas? Both are V12's, I wouldn't have it any other way .
Interestingly both share another problem. Alarm start inhibit prevents operation. The '95 is basically a parts car, the previous owners mechanic installed a ground switch to the security system to enable starting but then has to be shut off to prevent the alarm from sounding. It starts and runs but isn't pretty. The '94 was working fine until it didn't lol. Got stranded and held the ignition in the start position and cycled the gear shift between park and neutral to get it to start but that only worked once or twice. Opened up the center console to check the micro switches and they are working just fine. Unplugged them and put an ohm meter to the contacts and they would zero out when engaged.
Any ideas what or where else to check? Thanks in advance for any help.

Current:
94 and 95 XJS convertibles
Departed:
88 H&E convertible
99 XJR
04 XJ8

 

So I now have two problems solved and a new one arise. I noticed when doing a draw test with the ammeter the CD changer would cycle every time. This would happen even with all the main power nodes disconnected. Looking at the wiring diagrams as well as the changer I did not see any separate dedicated power to it so I figured it must be trough the radio. I pulled the 10A fuse for the radio and the current draw dropped to an acceptable .005A. Strangely the CD changer would still cycle when connected . Well, we'll see how the battery does by tomorrow.
As far as starting goes, I figured that someone would inquire about wether starter was working, so I did what I should have probably done first; went to the starter relay to short it to force the starter to operate. And it did but I also noticed that there was corrosion on most of the relay sockets in that section so I sprayed them with electrical contact cleaner as well as cleaned off the relay prongs and once replaced voila, the starter worked every time after that! Too bad that wouldn't work for the '95 car.
At this point I don't have a working radio. Both the radio and CD changer in this car are non stock units so who knows where they may have pulled power from to run them. Now I'll have to chase some more wiring to get that straightened out. But, hey I can at least drive it now.

 

Following, because I have a ‘95 Flamenco Red V12 convertible with the same electrical draw issue… I’ve always suspected the alarm system as the culprit but haven’t been able to figure it out officially.

 

First try disconnecting the three main power distribution nodes one at a time to see if it makes any difference in the parasitic drain. Put an ammeter between the negative cable and the battery. Red lead to the ground cable and touch the negative lead to the battery ground. Read the current draw. Do this first to note how much you have and then disconnect the other power points and check after each one is removed. As shown there are two power points, one on each side of the fire wall on either end of a bus bar and the one under the battery tray. Mine was showing 1/2 amp draw. If you find it drops to .04a or less after disconnecting one of them, then you have isolated the circuit. If not try pulling some fuses that you might think could be an issue. In my '94 the radio fuse killed it to .004a after which I did some rewiring that dropped it to .04a which still seems like it might be a bit high. I'll have to see how it goes. Hope this might be of help.
Another member posted the following schematic:

 

Following as I have a 90 XJS that dies if it sits very ong. Previous owner solved it by posting instructions to disconnect the battery if not driving regularly. I'm probably gonna sell it as I don't have the time to work on this.

 

Plug them into a battery saver when not in use...simples

 

Well, that would be true for long term or winter storage but with the power drains that we were experiencing it would only take a day if that to kill a battery. Something that definitely should not be. So far I've been able to use the car normally, I did sort out the radio wiring somewhat but I believe the problem may have been how the disc changer was loaded, as it was constantly cycling with one slot empty. Reversed the load of discs and it seemed to only cycle through once and quit even with one slot still empty. So now I currently only have a .04a draw instead of the .5a I previously had. Seems to have satisfied the problem for now. For extended sitting I like to use a small solar charger hooked to the cigar lighter and that seems to keep the battery topped off.