Resolved: - There are 2 large fuses in the boot (Trunk) and one of them had melted and was causing an intermittent connection.
Solution: New 500A fuse, new Fuse Housing to be on the safe side.

Hi Folks,

I have an interesting mystery, looking for some of you legendary problem solvers to suggest some ideas!

My 2004 XKR will not crank, when i turn the key I get clicks from the engine bay but nothing happens.

I have charged the battery and then tested it and it is perfect.
I have tried both keys and neither work.
Diagnostics is showing lots of errors (U2012, B1595, P067F, P2254) (usually that means battery is failing but not this time).

My only clue right now is that my cigarette lighter plug in battery meter is showing 11.7v with the key in position 2.
When I plug in my Noco Boost HD jump starter the voltage goes form 11.7v to 11.9v - still not enough to start the car.

My instinct is that there is not enough power getting up to the front of the car.
I have checked the 3 ground points in the boot are all are tight... BUT....I have a lot of corrosion on the rear (arches, below the lights, the usual spots).

So, what can I do to diagnose the problem? Anything else I should check? Any fuses or relays that might be the problem?

Any and all help is greatly appreciated!
(I have a multimeter but I am a beginner so if I need to do electrical testing please forgive me if I ask you to explain it to me like I am a kid!)

 

The voltage problem is probably the bulkhead connector. The battery cable runs from the boot to the engine compartment. There it is connected thru the panel to the engine compartment. Unbolt and clean and polish everything and then try to start again. If that doesn't work get back to us.

 

And also do a hard reset procedure on your battery. That worked for me when I had a similar problem back in the summertime....

 

Resolved:

Thanks for the help!! Avern1 - as soon as I started tracing the positive cables I found this:

Swapped it out and the car starts!

As there was some melted plastic I am going to replace the housing etc also.
£20 for 2 fuses and a new housing on eBay.

Thank you!!

 

Well done....

 

I would be careful leaving it at simply replacing these mega fuses.

A few weeks ago I discovered a lot of resistance at the lead cable going to and coming from this junction. During cranking, and while running, cable (and it really is a cable) was getting so hot that I couldn't keep my hand on it. Pealed back the insulation to find that water (or something) had entered cable, started corrosion, and the cable was producing greater and greater resistance (HEAT) over time.

I believe there is a junction for this cable on the RH side of the tunnel IN the car (under carpet and console), and from there it goes into the tunnel and up to the false bulkhead connector on the RH side of the engine bay. From there, to the alternator and starter...

When the HUGE dump of amperage goes to the starter for cranking and while the car is running and charging back to the battery, electrical resistance can grow in this wiring/cable and cook things pretty good...

There has to be a reason why so much heat grew at that mega fuse coupling. Gotta dig into it.

My fear was that things would get so hot, for instance in the cabin under the upholstery, that it might start a fire. It's HOT heat for sure. All that has to happen is that the insulation on that cable finally exposes the cable underneath to bare metal somewhere and the mother of all automotive arcs will be next.

Gotta keep digging.

 

That's a great point JayJagJay!!
I think it's worth a few hours of investigation to ensure all is safe!

Was a it a huge job to replace the cable all teh way through the car?
Is it a standard part or did you have to get a new cable made?

 

I'm still wondering if I'll have to... I opened the cable in the trunk pretty far back and used a bunch of vinegar and baking soda... Kind of untwisted the wire some (not the best thing) and got a copper wire brush to it. Hooked every thing back up and started the car and let her run. No more heat. Cleaned up that point in the engine bay on the false bulkhead and cleaned up the battery terms and ground - which was clean. Yeah, no more heat.

Later, while doing something else, I stumbled across the junction inside the car on the exterior of the tunnel on the RH side near the passengers knee area. (This is all from memory.)

I remember thinking it wouldn't be that hard to change once I found the junction. If I have it right that cable enters the car under the back seat, comes up the center of the car and to the area under the console before splitting off.

To my surprise, there were lots of used cables, it can be bought in bulk and,,, new for like a million dollars...

I know it ain't no fun ripping into the truck like that butt,,,, I would just check the part of the cable that bolts to that fuse and a few inches back on that cable - cutting the insulation back and heat shrink after. Put your hand on it just after you start the car and while it's running feeling for heat. Something was going really wrong there - the other side of the fuse looks new. Just my thinking - and I ain't usually the worrying type.

I would love to hear a report if ya find anything new out.