I recently posted a thread, dead battery, can't get trunk open, thinking my issue was a dead battery, as the Jag would not start and had no headlights and I could not open the trunk by electronic means. As it turns out, my issue is a much larger problem. Battery is fairly new and is charged.

My issue is verbatim this person had (linky). Unfortunately, that person returned their Jag to where they bought it from, so we don't know the resolution.

Here's what Jag exhibits :
a) Engine won't crank, no click
b) Dash lights come on, then most extinguish - CEL stays lit (no dash "ding" sound).
c) Radiator fans come on
d) Radio comes on and A/C + heater blower comes on, and horn works.
e) Headlights, wiper, tail lights, interior lights, interior trunk light, license plate light, blinkers do not come on.
f) Door locks do not respond to center-dash lock button and do not respond when locking / unlocking driver door with key; trunk unlock will not respond to steering column unlock or trunk fascia unlock button.

What I've done:
a) Checked all pertinent fuses under hood, left / right heelboards, and in trunk - all good.
b) Removed all pertinent relays and sprayed terminal / sockets with electronic spray and have "tapped" on relay with screwdriver handle (esp. those directly behind right-side headlights_.
c) Removed + cable lead from battery and waited five minutes, then reattached - still no power to components as in (e) above (this workaround worked for "Brad" in the referenced link above; i.e., various components would work and car would start - the thinking was that disconnecting the battery was "resetting" the various modules).
d) Sprayed electronic cleaner into ignition key hole yesterday; today, sprayed key and into key hole, dry lubricant. I do need to slightly jiggle the key to get it to turn to ON.
e) Bench tested interior trunk bulbs (they light) so they should come on in trunk, given power. I've also probed the trunk bulb socket with a meter and there's no voltage.

Quite literally, I drove the car one day with zero issue (not even a hiccup) and she sat for maybe 2-3 days, and now this issue.

I've done quite a bit of reading and think I have one of the following issues (though it's possible I have more than one, but i doubt it)
1) Security and Locking Control Module (SLCM) found in the trunk behind fuel filler tube.
2) Faulty ignition key / mechanism.
3) Bad relay (one behind right side headlights?)

Obviously, there might be something else.

Anyway, so what's the best diagnostics plan? Is there a way to bench test the SLCM? Relays? Ignition key mechanism? Should I test one before the others? My gut feel is a faulty SLCM, but I certainly don't want to run off and purchase one and it makes no difference.

 

I don't see how a fault with any one of your three candidates would cause of all of the issues your are seeing. Lights for example.

The list of things that work and don't would be pointing me at the BPM. Here's a quick list of what is controlled (or influenced) by the BPM.

Wipers
Starter Circuit
Gearshift Interlock Control
Headlamps, Sidelights and Fog Lights
Indicators
Courtesy Lights
Puddle Lights
All Audible Warning Chimes (May be not Air Bag?)
Seat Heaters
Windscreen Washer

Here is a list of things that are not controlled by the BPM

AC
Blower Motors
Radiator Fans
Brake Lights
Clock
Headlamp Levelling
Sunvisor Lights
Glovebox Light
Cig Lighter
Radio
Instrument Pack
Door Mirrors
Seat Motors
Horn


So if you can tick off some more of these in one list or the other it may provide more pointers. These lists are from a quick scan of the electircal guides and are not intended to be definitive.

I have also found from experience that the BPM isn't a working or not module. Some functions may work in the module while others fail.

The central locking could be the fly in the ointment. I don't think that is failure of the BPM. But you may have more than one issue. I have seen a number of threads over the years where a BPM failure has happened immediately after shanigans with battery changing/jump starting/charging.

 

I agree! Since replacement of the BPM is a very big deal, I would try to eliminate any other possibility before replacement. That would include looking for corrosion on the BPM connectors, making sure the three (I think) 12 volt supplies to the BPM are all giving solid supply, making sure the engine to chassis and battery to chassis grounds are clean and tight. If youi don't know how to check the 12 volt supplies to the BPM, at least assure the bulkhead power connections are clean and tight.

A few minutes with a voltmeter should give some better diagnostic benchmarks.

 

Thanks to Brendan and Ross!!

My flawed thinking was related to a "immobilized" scenario (mostly because of the no-start), but in hindsight, that only occurs with non-US Jags (right?).

Anyway, so I'll write up a comprehensive list of what works / does not and compare to what module(s) control what. But yes, I think ya'll have steered me away from the SLCM and concentrate on the BPM
.

 

I don't remember... have you had a go at the engine to chassis ground strap?

 

Checked it a couple of days ago - nice-n-tight, no frays. AAMOF, I've visited most all the + feeds and the neg. studs (loosen and re-tighten) and all look good.

I found a post or two out at JustAnswer (Richard - mechanic), with a step-by-step to test the BPM, i.e., using a meter to test the various pins on the three connectors. I've been pretty lazy as of late, so have not gone through Richard's procedure, but good to know it's available. From all my research of other folks having had the same exact symptoms, I blindly ordered a BPM from eBay this AM - should be here by the weekend. I'll report back on the results.

 

BPM came in early, today ~2pm. Removed battery to charge it, while I installed the new BPM. Plugged in the three connectors and secured the BPM in its place.

Secured the battery, put on + terminal cable and tightened it, and the moment I placed the neg terminal on the battery, the trunk light came on - good sign. Tightened terminal.

Climbed in driver seat, inserted key - ding ding ding, interior lights and puddle lights on.

Turn ignition to ON, waited until dash lights extinguished (CEL stays lit) and turned the key to start position . . . crank crank crank crank crank crank . . .

I can place my foot on brake and move selector to Neutral position now . . . crank crank crank crank crank crank.

The Central locking mechanism does not work. Key in door to lock does not affect other doors. Trunk release on dash and trunk lid fascia electric button do not work.

Well, so I have interior lights, I get the dinging, the car does crank, but does not fire up, and no Central locking. I've read about this. The BPM is replaced and the car cranks, but no start and no Central locking. More research I guess