To solve this issue I removed the right wing of the car
then I had to find from the harness where was the wire to the starter solenoid
finally I got it as shown here in this picture.



And than by chance I found it at the feet of the driver on the left side,
Also because I was looking at the best way for the cable to run from the front to the boot, and the harness down the feet of the driver was just there accessible since the carpet was removed (to access to the kessy).



Finally I found the same cable in the harness on top the left battery in the boot



So all the way the wire to starter solenoid is good meaning that the problem was inside the fusebox.

 

The Situation now is that engine starts but does not maintain idle and stops after 3 seconds.
Here is the diag report showying a lot of misfires

Address 01: Engine Labels: 07C-906-018-BEB1.clb
Part No: 07C 906 018 AR
Component: BY-6.0L-TT G ª6521
Revision: 36ÿTT Serial number: 000-00008.12.
Coding: 0000173
Shop #: WSC 00000 000 00000
VCID: 75B7E1C979D2C873504-5160

15 Faults Found
16455 - Sensor for Ambient Air Temperature (G17)
P0071 - 004 - Implausible Signal
18331 - Please Check DTC Memory of ECU Number 2
P1923 - 008 -
18320 - Pressure Sensor for Brake Boost (G294)
P1912 - 001 - Short to Plus
16502 - Engine Coolant Temp. Sensor (G62)
P0118 - 002 - Signal too High - MIL ON
16929 - Sensor 1 for Exhaust Temp Bank 1 (G235)
P0545 - 002 - Short to Ground
17837 - Circuit for Brake Vacuum Pump
P1429 - 004 - Open Circuit
18308 - Coolant Fan Control 2
P1900 - 004 - Open or Short to Ground - MIL ON
16955 - Brake Switch (F)
P0571 - 008 - Implausible Signal - Intermittent
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 001 - - MIL ON
16685 - Cylinder 1
P0301 - 001 - Misfire Detected - MIL ON
16689 - Cylinder 5
P0305 - 001 - Misfire Detected - MIL ON
16690 - Cylinder 6
P0306 - 001 - Misfire Detected - MIL ON
16687 - Cylinder 3
P0303 - 001 - Misfire Detected - MIL ON
16686 - Cylinder 2
P0302 - 001 - Misfire Detected - MIL ON
16688 - Cylinder 4
P0304 - 008 - Misfire Detected

-------------------------------------------------------------------------------
Address 11: Engine II Labels: None
Part No: 07C 906 018 AR
Component: BY-6.0L-TT G ª6521
Revision: 31ÿTT Serial number: 000-00008.12.
Coding: 0000173
Shop #: WSC 00000 000 00000
VCID: 75B7E1C979D2C873504-5160

4 Faults Found
19475 - Valve for Exhaust Flap 1 (N321)
P3019 - 004 - Open Circuit
16776 - Camshaft Position Sensor (G301)
P0392 - 002 - Signal too Low - MIL ON
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 001 - - MIL ON
16692 - Cylinder 8
P0308 - 008 - Misfire Detected




The ecu engine I reports misfires or 1, 5, 6, 3, 2, 4 cylinders. all these cylinders point to bank 1 of the engine. The bank 1 of engine cylinder 1 to 6 does not fire
This means that it is the full harness going to bank 1 (to open the fuel injector or / and pull the spark plug from the coil of these cylinders) that is probably causing the problem.
I went to the engine ECU compartment to check that the connectors were properly inserted after putting back the engine.

From my findings i conclude that the 2 engine control units are not connected as it should.
The control unit in the front has its big connector (on the driver side) labeled #2 and small connector labeled #1
while the control unit at the back has its big connector (on the driver side) labeled #1 and small connector labeled #2

additionally the 2 control units are just the same.
Control unit presently at the back


Control unit presently at the front


Then I submitted this question to Johnny Hotspur GT:
"which control unit do i put at the back as control unit #1 with its big and small #1 harness connected to it.
And as a matter of fact the same question for control unit in the front."
From his answer:
"Both ECU'S are the same, and being that nobody labeled them 1 and 2 when they removed them, I can not tell you now which is the master and which is the slave, and yes, as you said, 1 + 1 on one ecu, and 2 + 2 on the other ecu.
In the future, please have your men number the ecu's as 1 and 2 ."
after interchanging both ecus, BINGO! the car is now starting and running smoothly
idling is normal.
moreover engine ecu 1 and engine ecu 2 no longer report misfires.

 

Not sure if it's relevant to this but I had a series of misfires which turned out to be a number of the cables to the injectors had hardened over time and fractured when the intake manifold was lifted to replace the plugs.

 

​​​​​​Hello @steve.2.lowe ,
Good information as to the injector wiring, I had the same on my A8L W12, although I also had a little friend get at the wires..

As to Kilog's issue,
Maybe you missed the end of Kilog's post, he no longer has misfires, and the engine is idling normal now, it was because the ecu's were swapped as master and slave.

"Then I submitted this question to Johnny Hotspur GT:
which control unit do i put at the back as control unit #1 with its big and small #1 harness connected to it.
And as a matter of fact the same question for control unit in the front.
From his answer:"
"Both ECU'S are the same, and being that nobody labeled them 1 and 2 when they removed them, I can not tell you now which is the master and which is the slave, and yes, as you said, 1 + 1 on one ecu, and 2 + 2 on the other ecu.
In the future, please have your men number the ecu's as 1 and 2 ."
after interchanging both ecus, BINGO! the car is now starting and running smoothly
idling is normal.
moreover engine ecu 1 and engine ecu 2 no longer report misfires."


Johnny