What did I break???

[RossoDiamante]

On a M400:

So, I've gotten to the point of wanting to see if the tightening of the rear axle nuts in any way explains or cures my soggy brake pedal. The car had been sitting for 5 days. Tried to start it up. Sounds like low voltage. Fuel pump comes on but cranking results in no start and just clicking. Charge the battery during the day. Come home and the charger reads full. I disconnect the charger and go to have dinner and sleep. Next morning, car doesn't start again. Same thing. I hook up the charger/starter again and put it into start mode. Cranks but clicks and no start. Then everything goes dark. Now no interior lights, no radio, no fuel pump, no nothing.

I suspect just a fuse somewhere but is there something that cuts out the entire electrical system?

[andygtt]

when this happened to me my negative lead was loose on the battery, however a dead battery could exhibit the symptoms you mention, once they are flat they won't hold a charge.

[Midlifecrisis71]

Is it clicking or cranking, 2 different things ?

[RossoDiamante]

Was clicking. Now it's doing nothing!

[TuxMan]

On the chassis rail above the ECU (drivers side ) there is a back of 4 small fuses and one very large fuse , check them all .

[XLRONYX]

andygtt said:

a dead battery could exhibit the symptoms you mention, once they are flat they won't hold a charge.

What Andy said. I had electrical issues but didn't realize my battery was flat because it measured above 12 volts with no load. All the electrical gremlins (not sure what the UK equivalent is) died when I replaced the battery.

Do check all your fuses per the advice here, and check your alternator wires for crispy insulation. Heat from the front turbo will attack alternator wires and connectors.

Jeff

[RossoDiamante]

Thanks for all the suggestions. To close the loop, I searched for the 80A Main Fuse and couldn't find it. I see the picture in the installation manual, but that appears to be for the M12. The M400's location is different and I didn't see an accompanying picture. I see the "Rear Fuses" and the "Bulkhead Relays". But couldn't identify the 80A Maxi Fuse holder. Perhaps it is behind the turbo intake tubing?

Anyways, the culprit turned out to be a simple as the battery disconnect knob on the positive battery terminal. It must have slowly loosened itself and backed out a bit. When it backed out enough to prevent enough current from starting the engine, I started reaching down there to connect the charger clamps to the terminals. After a couple of manipulations I must have further loosened it somehow until it fully disconnected and that is what led to the dead everything state. I was just fiddling with stuff while trying to find the 80A Maxi Fuse and at one point twiddled the disconnect knob. I was getting ready to throw in the towel and consult the forums when I opened the passenger door to grab something and lo-and-behold the interior lights turned out. Surprised, I went around to the driver's side and tried to start the engine which fired right up, first try. Shut down and restarted -- no issue.

So it's "fixed" but I still have no idea where the 80A Maxi Fuse is on the M400. Can anyone point me in the right direction for possible future reference?

[M.Ako]

Sorry, I am unable to help, but glad she is up and running.