My wife’s 1990 XJ-S convertible had a battery drain problem when we got it in 2005. As a temporary measure I installed a battery quick disconnect to sort out whether it was a battery problem or a car problem. With the battery connected the battery would drain (10.5V -?) to where the starter wouldn’t crank the engine after 2 or 3 days of sitting. But with the battery disconnected the car could sit for at least 2 weeks or more and then start right up when I reconnected the battery (12.4V +?). So it was clearly a car problem and not a battery problem. Then with the help of this list, my digital multi-meter, and a lot of patience, I was able to successfully isolate the battery drain to the power radio antenna that was intermittently trying to lower itself from time to time, with the car off and the key out. Once I figured that out and isolated the power to the power radio antenna by disconnecting the wires to it in the trunk, again the car would easily start even after sitting for 2 weeks or more without being driven. I removed the power antenna from the car, disassembled it, and found that the controller circuit board was badly corroded from salt deposits (this car spent a lot of time in Florida before we bought it) as shown in the pictures. I am surprised that the radio antenna worked at all with all that corrosion. I purchased a used power radio antenna with a broken antenna mast, but nice replacement circuit board, from a Jaguar breaker on the east coast USA, swapped out the corroded circuit board with a nice new looking one, and that fixed the battery drain problem for over 10 years now. I left the battery quick disconnect in place and use that regularly when I do work on this car that require me to disconnect the battery. However, this car occasionally sits for a week or two without being driven and starts up nicely without any problems. If it sits for longer than that I will put a battery float charger on it to make sure it is ready to be driven.
I have read many times on this list where battery drains were caused by boot lights, security systems and other systems powered by the battery when the car is not running (like the power radio antenna) and the key is out of the ignition. There is always a cause for these battery drains and all that is required is a digital multi-meter, some wiring diagrams, and some time to pull fuses and isolate the drain source. In my case this was well worth the effort because other family members drive this car and it was an inconvenience for them to have to connect/disconnect the battery and input the radio codes in order to enjoy driving this beautiful car.
When I got this 1990 XJ-S convertible its battery was installed as the one in your picture shows, with the terminals towards the rear of the car with the negative terminal on the left and the positive terminal on the right. When that battery died I took the battery from one of my Series III XJ6 parts cars and installed that because it was free, handy, and in great condition (I think it might have been brand new). Interestingly enough with the terminals towards the front of the car and with the negative terminal on the left and positive terminal on the right, I was able to reroute the cables and get the plastic cover to fit over the battery with the battery quick disconnect still attached. I wasn’t able to do that with the quick disconnect that I have if it was located on a negative terminal towards the rear of the car because of the curve of the plastic battery shield is much closer to the battery on that side.
I have had it this way for years now and it works out pretty good. I like having the plastic cover over the battery as shown in the attached picture because others in the family drive this car and they put stuff in the trunk (boot) and I felt better about having the plastic battery cover in place for safety reasons to avoid inadvertent contact with the battery terminals.
Thanks for the detail, @Paul_M_Novak. That battery quick-disconnect is an interesting idea (thanks, too @Dougf1111). I really just need to find the time to pull fuses perhaps - tough with two young kids at home, but it’s gone from being a hard start after a week to seemingly being a REALLY hard start now. Seems to me my grandpa had the same problem many years back and found a short or something with the trunk light. There’s no longer a bulb, but is it possible there’s still a draw there somehow? Do you have a recommended multi-meter or will most anything do? And do you have a good wiring diagram I can use? I’m a real newbie for sure, so I appreciate your help.
Well, I tried to upload a couple of electrical guides (PDF uploads are supposedly allowed), but it didn’t work. Nor could I figure out how to message you to ask for your email address or give you mine. Maybe someone else can figure out how this new website works.
Not working for me, Robin.
I click the Avatar and the “message box”, then navigate to the PDF file and double-click, and it shows its name in the message box, but when I click upload, nothing seems to happen, the filename disappears and I’m back at square 1.
Hi Robin, I sent a PM to Beau, and received a “Thank you for the offer” but no e-mail address. I have sent (and received) several very helpful Jaguar PDF files in the past, but without the address I guess I can’t be helpful!
