I will be checking the manuals that will explain why my 95 XJ6, which has been running well for years, ac blows cool, new battery....and no real issues....drops dead at parking lot speeds in...thank goodness...in a parking lot where I could pull her over. No engine, and no power to anything at all. Not even the hazard flasher. ??? As it turned out, I was still waiting for the tow truck an hour later...and it's hot as hell right now in Central Florida...when I heard the radio start up (which is wired to work independent of the key)...And, power is now back on; the engine started up like nothing had happened, AC began to blow cold. So...I chose to drive home rather than wait another hour for a wrecker. Got home with no issues but it was so hot my rear mirror glue came loose about twenty minutes before the front mirror assembly did the same...it was HOT today. So what component could kill the entire electrical system...and then come back after sitting for an hour... perhaps from cooling off? I just took this car out late at night and returned over a high bridge...if this had happened then and there with no lights at all.....!!! Help!

 

Chill out

With the engine turning you have 2 power sources at once and if one falls out you have the other until the battery drains , voltage gauge ?

With the heat you may have an open cell on the new battery , heat expansion / swelling

Do not over tighten the positive battery post bolt / do not install the battery in backwards in your frustration

Ask me how I know .....................................twice

Around the slow speeds the on the transmission connector can be contaminated causing the transmission ECU and engine ECU not to dance together as they coordinate / regulate their dance , this connector shows up at coming out of park speeds

There is a trick to the on transmission connector removal without damaging it

 

Alternator fault red instrument cluster light ?

It is not square in my head where the voltage value gauge reads as a test point

The alternator red light comes straight out of the alternator / voltage regulator inside the alternator

A good alternator will read 13.5 to 14.5 at the gauge and if alternator faulting it will read battery voltage ( if fully charged 12.75 )

You can mark the gauge with tape to keep track of your values on a test run

The gauge is very accurate after a starting sequence / recharge time

 

The crash / inertia switch can trip for no reason , you can jumper with a paper clip the 2 white wires on the connector , this would as the switch tripping kill the fuel pump and some other things ( but not total power failure , your stereo wired hot at all times )

The fuel pump relay can drop out , but your description is no cranking as in total power failure ?

The fuel pump relay " control " power is fuse # 10 right heelboard fuse box , this fuse requires the right heelbard king relay in the corner of the fuse box to stay closed

This right heelboard king relay can be swapped with the left engine bay fuse box king relay ( in this instance only it only runs the car horn so swapping option )

 

The proper way to test for a open cell is hit it with a wooden 2 X 4 with a meter ( voltage ) as the battery is disconnected

The fault may not show until battery heated up

 

Haven't gone to the manuals yet, but still no logic about how ignition and all power to the car disappeared in a split second with no warning at all. No stumbles...just all power gone while running great for two years. Not even the hazard switch had power...I checked the net for any peculiarities with the AGM battery I have, but found they generally like heat and have no history of instant failure! Somehow the main power went to zero...while I had no visible gauge issues: temp, oil pressure, both OK and voltage was great right under 13. And after I went inside the cool store for about an hour, I came out and the radio was on! It healed itself? I then drove home no issues...but thinking it could die at any time instantly. It's possessed.

 

Both the alternator and battery depend on the ground negative post on the battery and the stud on the chassis , may have been disturbed on new battery install

Right under 13 volts ( just above fully charged battery 12.75 ) is an underperforming alternator voltage regulator

You may be looking at 2 problems , the alternator can be totally failing being masked by the fully charged battery voltage and then it fails

Voltage regulator part # IN435 , I wouldn't trust the ones on E - Bay from my experience

An auto parts store alternator test is free

# IN435 Voltage Regulator for Denso Alternators, 12 Volt,On: Asuna (1993-1993) , Geo (1990-1993) , Isuzu (1990-1993) , Jaguar (1993-1997) , Jaguar - Europe (1994-1997) (alternatorparts.com)

 

Did this happen when changing in or out of Park ? I’ve had issues with the park sensing micro switch, but that’s when trying to start, not when car is running.

Hope the mystery is solved without too much expense and head scratching.

Alan
96 3.2 Sport.

 

No, it happened moving at about 8 MPH allowing me time to coast into a parking area...how convenient! I can't think the alternator or the new battery were the issue...the car sat for days quite often without running and the system was never run down. It all went south in a split second with no indication on gauges or dash lights...and then all power returned after sitting for at least a few minutes up to an hour? Strange. The suggestion of it might being the voltage regulator makes sense...what else can die instantly that would kill the ignition and all power? And then heal itself? But of course...it's an intermittent problem. The VR is cheap...may buy one and at the least it serves as a backup for all three cars...thanks for the comments, folks!

 

Before changing the VR look at the product of the VR as the alternator output heavy cable nut tight tight

You can see the nut from the top through the intake pipes on the starter solenoid through connection to the rest of car plus the one on the alternator

Someone had excellent pics looking for

The alternator and battery charging is dependent on the heavy battery cable terminal post attached to the inside the engine bay right wheel well rear ( about 4 inches from rear engine firewall

You would have to remove cable and wiggle the bare post without the attached cable restricting wiggle movement

Before reinstalling alternator , the auto parts store has a spin up machine to test the off car alternator

The VR must be powered by fuse X and a connection ( Papa Indy 1 or Papa Indy 61 pin Y ) of an external connector that was subject of a TSB , the fuse should be good if alternator final power comes back

Still looking for through intake pipes nut pics on broke computer

Gotta go to Dialysis for a while

 

" Did this happen when changing in or out of Park ? I’ve had issues with the park sensing micro switch "

The park switch can be tested if with your fingers on the ignition switch key barrel clicks in your fingers as you slightly move the shift lever slightly out of park shift lever park gate

 

I tried to find the excellent pic someone made of the first connection from the alternator B + output battery cable at the tie point sometimes loose nut connection as you look through from the top between the intake pipes

But I have this one

VR power wire fuse # 10 right engine bay fuse box ( fuse # 10 should be good as apparently the alternator comes back alive to charge the battery ? )

What I said earlier about the Papa Indy 1 and 61 connector being in the VR power wire is wrong

There are problems with this fuse but that's if it blows as a tell

There is a mega fuse ( loose terminal nuts found ) located under the rear seat pan but that's some work to removing the rear seat pan ( fuse / terminal nuts hidden under a black plastic cover )

If you do remove rear seat pan do not drag seat on rear door felt trim

This would be the point I have marked 13.5 volts on the print

The aft blue terminal end goes back to the battery , the fwd blue terminal goes fwd to the alternator via the terminal post on the right wheel well and the starter solenoid tie point upper terminal post

The yellow terminal is where the power returns back fwd to the rest of the car fuse boxes ( minus the trunk fuse box ) ( then we come back around to the instrument voltage gauge test / pick up point location ? )

There are also mega fuse terminal post nuts right at the battery positive post

Under the rear seat pic

 

OK! thanks for all the alternator/ground/power details...I had read somewhere, perhaps in details for an earlier car, that the inertia switch only turns off power to the fuel pump, but on the 1995 it also kills all ignition circuits (which means virtually everything is turned off!) and other things...so in fact this all might be due to a faulty original inertia switch at 27 years old which in my case costs $31.00 delivered and is fairly easy to swap out. I see no evidence of poor charging at all...just that crazy halt of the ignition and all power for a few minutes...will advise! Strangely enough, the one for the 1996 is over $160.00 through the same source. But I pulled one out of a 1995 parts car to look at it and the one I have coming is the same number...

 

You can jumper the inertia switch connector between the 2 white wires with a paper clip , works for me and is very low current so no arcing hazard

This inertia switch drops out a few of the king relays in the corners of the fuse boxes

There is a simple exercise to test full car power distribution control by feeling these relays ( 4 ) click back to open as you remove them with the key on, engine not running ( with the exception of the 5th left engine bay fuse box king relay ) runs car horn

But your observed your hot at all times wired stereo is a tell that you lost the battery and then came back ( after cooling ? )

There are 3 fuses / power pins to the stereo head so which component of the stereo drops out if you can tell or remember

In stereo install there is a ground wire stud somewhere in the area that could have been disturbed , this single ground wire if bad will drop out your fuse boxes king relays ( including a starter enable key / ignition switch ground path ) and will defiantly kill the running engine as specifically the right engine bay fuse box king relay and the fuel pump relay closing power as the right heelboard fuse box king relay

This ground path is pin 5 of the ignition switch connector as I found green corrosion on my pin 5

This is the switch side of the connector and switch does not need to be removed , your focus is the car side connector which lifts straight up to remove from dash mount out to you , if you have to replace the ignition switch you don't need a new key barrel or key

The 5 pin wire is probably color Black , confirmed

 

For me the biggest clue is that your hazard lights didn’t work. They are not dependent on anything other than the battery, and their not working, as well as your direct wired radio not working would take me to the boot / trunk area, as the most likely source of a total loss of battery power.
The extreme heat and the fact that you had recently fitted a new battery would certainly make me question whether it had some sort of manufacturing defect like a cracked post?
Beyond that, I would be checking for any connections which could have been pulled apart by expansion in the heat?
Might it be worth trying to recreate high boot temperature with a hair dryer?

 

There is a battery shim ( real cheap ) that makes up for the stretched from age positive battery cable terminal lead clamp , and maybe undersized new battery post

But you than again not over tighten the battery positive post bolt , splits the special C saddle nut underneath

Install the shim ( on the inside ) with ? corrosion preventive but conductive

 

I am having a heck of a time buying the correct OEM part that I think is causing the unpredictable, intermittent, but complete power failure in my 1995 XJ6: the part number is LHE6520AA, and I placed orders with two firms only to get a response later that the part is no longer available. Only used ones are on EBAY....and who knows what that buys...due to age, it could have similar issues. And folks, I don't want to drive my car when instantly at any time it could drop dead, lose all power; lights, etc. This is a major issue now that our cars are 25 plus years old...is there an aftermarket solution that is cost effective...who has used an aftermarket inertia switch with good effects? Or where in heck can I get a new one? Jaguarparts does not have it. Is anyone planning to make it again? Help!

 

Well, I would eliminate the inertia switch, at least until I know that it is the problem. Unplug it, connect the two harness pins together and drive it. If it fails again, you'll know it's not the cause.

 

Have considered that. Long term I hate to bypass a safety system but....

 

There is a full car power distribution test you can do as a one-person operation

This is your car power distribution in a nutshell

This would be minus the inertia / crash switch that drops out a few of the king relays in the corner of the fuse boxes , this inertia switch can be fickle as my own experience and others from reading

The inertia switch can be jumped with a paper clip with the 2 white wires , works for me understanding it is a safety item

The test is this :

Have the key in the run position ( engine not started ) and remove or rock the king relays in each of the 5 fuse boxes with the exception of the left engine bay fuse box ( only runs the car horns so this relay is a swapping option )

If you open up the inertia switch , spring loaded parts will fly everywhere , ask me how I know