Apart from the ongoing problem with my CD the car has been running great, I was out in it all day yesterday doing several stop / start errands, at the end of the day I topped up with £40 of Shell ultra and drove home without incident.
This morning I try to start the car and the dash panel is completely dead, no warning lights, no buzzing, absolutely nothing working on it except the odometer read out, and it won’t crank over. The only thing I can hear when I turn the key is the ABS relay click and the pump running for a few seconds as normal.
The battery is almost new, it reads 12.9 V and I also tested it on another car just to be sure.
I’ve checked every single fuse in the L/h and R/h footwells and all those in the centre console. When I pull the fuse marked 'instrument panel ’ the odometer reading goes off so I’m assuming that part of the circuit is ok. I tried swapping the EMS relay on the bulkhead with the similar A/C relay but it had no effect. I checked the ’ cut out ’ in the footwell to see if it had been tripped but it’s ok.
The Haynes joke book shows an ‘ignition on relay’ and shows the location to be roughly where the centre console area is, does anybody know exactly where that relay is on my 93 MY so I can check that. Any suggestions as to what to check next would be really appreciated, it’s completely baffling how a fault like this can develop with the car just sat overnight after running perfect the day before.
If it’s any help, the central locking is fine, the horns work, the sidelights work but the headlights don’t.
I’ve re-read Laverde’s post who also has a dead dash display but his car turns over and runs so I don’t think we have the same problem.
Hi Casso. I think a lot of electrical problems can be fixed by cleaning all the ground points, battery terminals, and checking all the soldering joints in every relay module, in the fuse boxes. It also helps if the battery is removed from the car and recharged every 3 months. How old is your battery?
BTW, didn’t you know our cars have their own mind?
Casso, the ignition on relay was behind the radio in the center console until it was relocated to the firewall. Exactly when that occurred is unclear. From the archives:
Grim and mystifying situation, eh? Were you poking around behind the radio? Maybe you dislodged a plug? I know I did that once and even went as far as pulling out the tank and replacing fuel pump before I located the plug that I’d dislodged the week before when trying to repair the blowers …DUH!
Anyway, good luck, sounds like a bit of a head scratcher for sure ,
Casso …
Everything you are experiencing sounds like a classic example of a dead battery to me. Did you try jumping it with another running car? You can’t check a dead battery with a volt meter, 12v means nothing it’s the cranking amps available that’s important.
The battery is wired directly to the starter through the starter relay that is energized by the ignition switch. The fact that the ABS relay is clicking when you turn on the ignition tells me the starter relay is working and energizing the battery and all the low draw items are working but there is not enough amps left to turn over the engine or turn on the headlights or other high draw items.
Batteries do that, perfect one minute and dead the next (go figure) even if the are fairly new. After you jump or replace it when you start the car make sure to check that the alternator is working properly, this you can do with a volt meter.
Hi Groove,
Thanks for the input. I agree it sounds like a failed battery, it has all the symptoms of a failed battery, but I removed the battery and tried it on another car, it cranked the engine on my Mrs car really fast with no sign of slowing or dying. Also, the dashboard is COMPLETELY dead, not even a flicker, no warning lights, no gauges moving, nothing. I think if there’s enough amps to operate the ABS pump then it would at least illuminate the dash.
Tell me about it 
I haven’t attempted to remove the radio/ head unit yet so no poking about behind there so far.
Mike. I’m fairly sure I’ve identified all of the relays on my firewall, none of them is the ignition on relay so it’s looking like it could be behind the radio head unit. It has to come out anyway to investigate the CD problem so I guess that will be my next move. It would help if I knew what I was doing but I’m hopeless when it comes to understanding the wiring diagrams for this car. I’m mostly working using my own logic, ie guessing that the ignition on relay powers the dashboard when the key is turned.
Casso …
Make me happy ad get a set of jumper cables and try that first.
Casso, depending on how accessible your car is (that is, assuming you can access the jump start terminals under the hood/bonnet), Grooveman’s suggestion makes sense.
If the jump provides no joy and further troubleshooting is required I can try to shed some light on the wiring diagrams. You are correct that the ignition on relay plays a role in the operation of the instrumentation (“dashboard”), but it is by providing a ground path, not by providing 12 volt battery power. The instrumentation receives ignition-switched power via fuse 9 (3 amp) in the center console fuse panel.
HAPPY DAYS ! I’ve found the problem and fixed it. I took the passenger side fuse panel out from the footwell and found a cracked joint around the 5th fuse down in row 1. It’s a 3 amp fuse and protects the ’ Lighting Logic ’ according to the details on the rear of the cover. I’ve reflowed the entire board. AND as a bonus my CD player is now back to normal too I’m sooo happy.
Thanks guys, you’re help is always invaluable.
Casso, that is FANTASTIC news. So glad you found the problem and posted accordingly. This is bound to help others down the road. Now go reward yourself!
Casso et al, I just had a look at the 1993 electrical guide, and this will help clarify the cause / effect relationship IMHO:
Note that fuse 5 also services the ignition on relay and the radio memory.
Cheers Mike, that certainly clears things up. The legend on the inside of the fuse box cover only states ’ Lighting Logic Control ’ for that number 5 fuse, no mention whatsoever of the ‘ignition on’ relay so I was a bit confused how fixing that cracked joint had resolved the 'no start and dead dashboard etc. I never stop learning about this car, not sure if that’s a good or bad thing
Be advised also if you add a aftermarket radio (with the dancing mood lighting mode) it may blow that A5 3A fuse. It happened to me after about a week after install, as I was testing all the new features. Now I just run the radio minimalist mode and have a hand full of fuses ready if I need them to get me home. Thanks for reminding me about the fuse box solder as something to watch out for also. There is also a module behind the glove box that sometimes need resolder for ignition issues.
Casso …
Who needs jumper cables anyway 
Amen, brother, amen! I don’t know whether Jag ownership is an automotive passion or some sort of perverse religion. Either way, I guess I’m hooked!
Grooveman, after reading your post there was a set of jump leads on the way to my house to try next, I’d loaned them to a mate about a month ago and rang him to ask if he could drop them off.
I hope your car is running sweet, did you manage to find a new condenser for the A/C ?
the ultimate question is… why the joint went bad while the car was sleeping in the garage? the possible answer is that when the circuit was energized the temperature of the joint was higher and with the small dilatation of the joints the contact was possible, but after it cooled down the contact was no more present.
I suggest the use of a termal image camera. A good one can show all the fuses and cables that are working and conducting current just in seconds.
It’s well known among the XJ40 owners on this forum that dry / cracked solder joints can be a problem. Even the youngest cars of this model are now 30 years old. Small Vibrations during driving, expansion and contraction from constant heating and cooling, and the fact that the earlier cars suffered from poor quality control in this area all contribute to this problem.
So far I’ve been fairly lucky in this respect, it’s the first time I’ve found a cracked joint on a fuse panel, but in the past I’ve found them inside a couple of control boxes, the last time it was in the ‘H’ box that controls the interior lighting as well as the side lights.
I would love to learn more about this component with the cracked solder joint. Anyone have photos to illustrate? I’ve been lucky with my car, not had any so keeping my fingers crossed.