Can the current usage by Speedo-Meter when car is switched-off which can drain the battery completely overnight

If the only issue with the radio is that it will not turn off and then drain your battery, I would locate the power wire to it and put an on/off switch on it to manually do the deed . Repair not cost effective. Make sure it is the radio responsible for the drain. Use an ammeter to check power usage with ignition off and radio connected and disconnected to just make sure.

Did you let the vehicle sit for 30 min. before testing ? Modules need to time out (go to sleep - power down etc.. How are you testing ? Have a ammeter inline with battery negative cable and negative battery post . Have any doors open ( door switch closed ) Key out of ignition ? How much current ? 50 milliamps max !

Start by having the battery load tested, it sounds like you have a bad cell.

I have less than fond memories of tracing electrical troubles in a Jaguar (though much older than yours). Here's the basic process you need to follow:
1. Pull all the fuses. Does the battery drain overnight?
If yes, then a circuit that is not fuse protected is the problem. Start with starter/solenoid, etc. Disconnect each thing and test with meter.
2. If battery drain stops, then use meter to check current drain on each fuse. One will have more than a trickle.
3. Once you find which system is draining, you can narrow it down further by disconnecting each thing on that circuit.

Yeah, It's a pain, and may take days, but you can find it.

You need to check for draining of battery such as glove box or trunk light on that you are unaware of.
Need a tech to check draining with ignition switch off. If you are capable, add current (amp) meter in series with positive battery cable and read if current is flowing with ignition switch off, then find out what is normal flow when car is off, ask dealer or check on-line.

Switch your Digital Multi meter to DC AMPs. Amps is usually indicated by an "A" on the Multi meter Switch. AC is usually shown as a "~" symbol and DC shown as a "-" symbol. You usually have to move the multi meter positive lead to a separate socket on the multi meter to check for amps. Sometimes there are 2 sockets, (a high range and a low range). Always test on the highest setting first. For example: High setting on your multi meter may be 10 Amp. Test on the 10 Amp setting first, then if the current drawn is less than your Multi meter's (low setting) move to that setting and keep testing. For example: On my multi meter the low setting is 0.3 Amps. Also indicated as 300mA (mA x 1000 = A).

Remove the battery's positive cable.

Connect the multi meter's positive probe to the battery's positive post while simultaneously holding the negative probe from the multi meter up in the air, to keep it away from anything metallic.

Place the negative probe of the multi meter on the end of the removed positive cable to complete the circuit.

That's right, you're putting a negative on a positive, but its ok, because if the drain is severe enough, you're most likely to blow a fuse or two, which will identify the problem area.

Above I said to remove the positive battery cable because that is the way I do it. You can do the same test with the negative battery cable removed. In fact for you that may be a better way to do the test, because there would be no way for any electrical issues to occur by accidently grounding the negative probe from the multi meter. i hope you understand what I'm saying here.

easy find and fix. if you have 1 tool, an ammeter. (DMM)
this is called (AKA)
dark current.
or phantom drain,
it means, simply, SOMETHING, is not turning OFF.
so in the dark look for glowing lights. look an all places.
glove box, too, compartments... ALL !
if no lamps on, then its something else.
all cars have 2 power feeds.
1: switch power (key switch)
2: hot all the time. (bingo there)
some lights are hot all the time, Head lights, dome.
and the alternator.

here is a page dedicated to finding it 3 different ways !
no meter, with meter or a test light.
all cars work the same (power DC) but parts of it are moved
about to make it challenging.....

http://www.fixkick.com/drain/drain.html

the first trick is to measure the drain.
then pull fuse 1 by one until you find the branch that has a drain.
keep i mind, 1 fuse can run 10 things....

Take out the battery and have it tested. Test should show what is wrong with it. If it is too old, then you are in for a new battery.

Hi there

Dont know the car,but its about the correct current for a lamp.Check the boot light switch ,it is normally the only one people dont check.

Otherwise connect an amp meter inline with the battery and remove some fuses ,one at a time until the fault is gone ,and then you will know what circuit it is.

Please leave fair comment if you think I have helped.

Thank you

Try to check the battery maybe your battery is over use or you need to replace the battery or check your alternator and check the fuse of the car.

I’m happy to assist further over the phone at https://www.6ya.com/expert/ramy_d9e7ebea3891f482