Help trouble shooting an electric problem after overheat

[trader2318]

I have a june 2001 build e38 with 165k miles on her.

It has been a joy to drive with no major mechanical issues over the last 70k mile of ownership and sees regular service changes.

My son recently started driving and he has been driving my 740i. That i will call problem 1.

The water pump failed while he was driving, which lead to a MAJOR over heating event.

I changed the pump, thermostat, hoses, etc which fixed that issue. From that point, for about 2 weeks with daily driving of about 40 miles, all was fine.

The second problem is electrical.
When an attempt to start the car is made, one of 2 things happens:

1 -the car starts and all gauges, and dummy lights read normal. What does happen is there is a loud cracking noise, resembling feedback, only coming from the rear deck speaker(woofer) on the drivers side. The feedback is rpm related, meaning that it get higher/faster with higher rpm. I have unplugged the power to the stereo in the trunk and this sound does NOT go away. The car can be driven, you just need block out the winding, feedback noise.

2 -When an attempt to start the car is made, the entire car goes dead.... all dash/interior lights go off and the starter will not turn. From this point, the only way to get the car to start is to disconnect the battery, wait about 30 seconds, reattach and she will start...with a driving experience explained in scenario 1.

My guess is that a wire has been compromised when the car overheated... As finding the wire is hunt and peck I would lover to be wrong on this.

Is there a way to attempt to isolate the circuit that is causing the problem, thus discovering where to initially look?

Any insights in to how to go about finding the problem wire.

Any guidance would be greatly appreciated. Need this car back in normal working order...fast.

Thank you for your input.

[psjr]

1. Sounds like a dead amplifier. Located in the trunk. Replacements may need coding.
2. I have only heard those symptoms 2 or 3 times, and all of those times it was a loose battery cable that someone forgot to tighten on the battery.

[trader2318]

WELL DONE SIR!!!

The buzz is gone. Ground cable was loose so that seems to wrap it up.

Thank you.