My XJS is garage bound for much of the winter and the battery only holds it's charge for about 3 weeks. It charges fine and holds all summer. So I think the charge simply leaks over time.

I bought a generic Napa battery cut-off gizmo, but on reading the instructions, it suggests a fused bi-pass to keep the clock and door controls active. This makes me wonder if there are any other Lucas secrets hiding in the system that I will unintentionally fry or reset or? by installing the switch.

Anyone have any knowledge/experience with this gizmo? Any thoughts on what size fuse?
Thanks for any suggestions,

Marshall Moretta
'96 XJS 4.0 Convertible

Submitted by asimko@netsolnj.com on Sun, 03/11/2007 - 07:15

The cigarette lighter device will never give you enough power to trip the door locks. the solenoids are a high current device. we just became aware of the device you mention because my wire takes her jeep to a jiffy lube, where they insist on removing the battery terminals to clean the connections, causing the need to reset time, radio stations, etc.

if i were going to store a car, i would take one the the cigarette lighter devices and attach an external battery pack to it, with either 8 D batteries,(a radio shack item) or (1) 12v "gel cell" like you would use for an exit light, or (2) 6 v gel cells. This device should have a fuse!

an arrangement lilke this would give you enough power to even trip the solenoids, so the door locks would activate. The cigarette lighter is fused with at least a 10 amp fuse.

of course the polarity of the batteries has to be correct. '59 MGA (sold)

Submitted by mghirsch@netzero.net on Sat, 03/10/2007 - 19:30

There is always a constant draw on the battery. There is the radio, clock, alarm, and possibly the ECUs. The alarm is spposed to be the biggest draw, but, IIRC, there is a sensor on the alarm that is supposed to shut it off if the battery goes too low.

THe switch you show will isolate the battery. But it will mean that everytime you reconnect it, you will have to enter the code for the radio. If your ECUs have learning capabilities they will have to start learning anew. Also, the ECU for the seats will loose it's programmng.

Before I installed it, I would measure the draw. Disconnect a battery cable and put a VOM between the terminal and the cable and see what it reads. It's possible you have a draw that is not supposed to be there, such as a light on in the trunk.

Installing the switch for the door locks, etc, will defeat the reason you want to install the switch. The draw seems small enough not to blow the fuse so the battery will still drain. The idea behind the fuse is as stated in the instructions with the idea if someone tries starting the car with the switch open, the fuse will blow and the car won't be able to be started, ergo a thief couldn't drive it away.

Maynard Hirsch
94 XJS v12 Coupe
86 XJ6
91 XJS (RIP)
78 MGB
67MGB

Submitted by windsor@hiwaay.net on Sat, 03/10/2007 - 19:29

Marshal:
For the last ten years I have used simple cut off switch on my 1994 XJS, which meant having to reset the radio ect. every spring, However, last year I found in the good old JC Whitney catalog, "a simple device" that fits in the cigar lighter socket, called a computer memory saver. This worked very well and was able to start it up every couple of weeks with just a screw down of the disconnect. I NEVER LOCKED THE CAR SO I DON'T KNOW IF THERE'S ENOUGH POWER IN THIS DEVICE TO LOCK OR UNLOCK THE DOORS. but it does do a good job on the memory functions of the car.

Both items are listed in the JC Witney online catalog as. COMPUTER MEMORY SAVER AND GREEN KNOB BATTERY DISCONNECT.

Windsor Davies
94 XJS 4 liter
90 XJ6