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