Here's my story.
Background: I've owned my 2006 XKR since 2010 (42,000 miles on the odometer) with no problems except intercooler pump in 2011. I haven't driven the car much in the last three years and decided to flush the cooling system along with changing the serpentine belts (supercharger and drive) and a brake fluid flush.. I removed the negative lead to the battery because I was removing the fan pack to get access to the belts. I reconnected the negative lead to the battery after taking the negative lead and holding it to the positive battery post for ten seconds. The car's electrical systems started acting like Lucas the Prince of Darkness---sorry about the reference but I owned a 67' MGB back in 1971. The battery was replaced in 2019 with Interstate MTP. I keep the battery on a battery tender and the previous battery lasted ten years because I keep them on a tender. I'm getting 12.6 volts at the battery and the same voltage in the engine bay at the engine compartment fuse box and engine management fuse box. The coolant has been drained (five quarts) and the brake system has been flushed/bleed. The shifter is locked but I can move it when the inhibitor is depressed. The instrument lights will come on with erratic flashing and a "system check" but nothing else will work (no headlights, horn or windows). Every time I open the driver's door the window will go down a few inches but I can't control with operator on door. I've cleaned the battery connections and the battery is fully charged according to my battery tender. Tomorrow I will clean the positive cable to the main bus and negative cable to the car along with checking fuses in the trunk (boot) and engine compartment. The interior and trunk lights were dim at first but they seem bright at this point (I'm thinking ground connections could be a culprit). I appreciate all ideas at this point but will continue to explore possible electrical connections. Any ideas from the brain trust are welcomed!
Thanks, Mike (Mountaincat)

 

Also remove and clean the ground strap connections between the bellhousing and chassis.

 

Another idea that hit me, could this be related to a failed brake switch?? I had someone in the drivers seat pumping the brakes for the brake flush and maybe the infamous brake switch might have failed.

 

I doubt that a failed brake pedal switch would prevent the engine from starting up....

 

The verdict is in---dead battery. Praise the Lord! Jon, I agree with you, but I thought I'd throw it out there. The battery had the right voltage but had no way of load testing it until I took it into a parts store. It just so happens I had the boat battery in the garage on the battery tender and I looked over at it and said what've I got to lose. The negative lead had just enough length to make the connection and 650cca. Filled the cooling system and turned the key and Miss Kitty purred once more. I did clean the ground connection between the bell housing and the body per RJ's suggestion but that wasn't the problem, although it was a good suggestion and glad I saw it while the car was up on my Quickjack. By the way RJ, my brother has lived in Douglasville since the early 70's. Thanks again for your kind responses and will never use a Interstate battery again since it lasted 3-1/2 years. I was under the impression that Interstate was a good battery. I'm not sure who manufactured the MTP-49/H8 since Interstate sources from several manufacturers including Clarios (Brookfield Business Partners) which owns the old Johnson Control brand. I'm probably going to pick up a Duralast Platinum AGM from AutoZone. Go Tigers! (that was for Jon)---of course who knows where Dabo and the Tigers are headed these days.😫

 

Dying batteries cause so many problems with these cars. There was a situation in the S-Type forum years ago where a guy had his ZF transmission replaced before he finally took someone's advice to replace his battery. The new battery immediately fixed his problem but he was still out more than $6,000....

Sadly, 3.5 years of battery life is not unusual these days, especially for a vehicle that is rarely driven. Quite a few folks on the four different automotive forums I utilize recommend a battery replacement at 4 years. Good luck with your new battery. I have had success with NAPA AGM batteries during the past few years. They were built by East Penn....

 

Here's "the rest of the story" on my battery replacement. I purchased a Everstart Platinum AGM battery H8 from Walmart for $169.84 which had a "Made in Germany" sticker on it . Based on what I've read it appears to be made by Varta which is owned by Clarios which purchased Johnson Controls. The serial number on the battery starts with JCH. You got to love the global supply chain. 🙄

 

Did the new battery fix your issues?

 

Sure did---I hope I can get more than four years since the battery comes with a four year replacement warranty. Just finished flushing the cooling system (six times) with new upper radiator hose, thermostat, resevoir (with new ear clamps) S/C and main drive belt. Took her for a long test drive and she ran great with the exception of the unbalanced tires. I'm going to Discount Tire in Hickory, NC to see if they can get the Continental Extreme contact tires balanced since the Asheville store has failed twice. I've gone to Discount for all our tires over the years---let's hope they can get it done. I must admit the car puts a smile on my face when I drive it. Got to get it ready for my daughter's wedding next week in Durham because it's the bride and groom drive away car. I'm thinking I might sell it and replace it with an F-Type???
Thanks, Mike

 

Make sure the Discount Tire store you utilize has the Hunter Road Force Balancing system. It has never failed to perfectly balance the tires on all of our vehicles....

 

Jon, great question. I thought all DT stores had the Hunter Road Force balancing machine, but saw on their website that some stores may not have them. I just confirmed that the Hickory store does have the machine. It's also nice to know that their regional office for the Carolinas is located in Huntersville, NC which is an hour away from Hickory. I remember your XK8 has some miles on it, have you had any front suspension work done on it? My car has 43,000 miles on it and not sure if I need to look at replacing some of the bushings based on age.

 

Have the front upper shock mounts been replaced?

 

Mike,

My wife's 2006 XK8 (now approaching 126,000 miles) got new Bilstein rear shocks in October 2014 (at Wayne's house in Spencer), new Bilstein front shocks / bushings / Welsh front shock mounts in January 2016 (again at Wayne's house), and Wayne's custom-made front shock mounts in June 2022 to replace the lousy failing Welsh ones (again at Wayne's house). At your mileage you probably do not need new shocks but if you have never replaced your front shock mounts, you should install a set of Wayne's custom-made ones. Over the past couple of years Wayne and Steve have created the best XK8 / XKR front shock mounts on the planet....