vz ss electrical faults

[ryanss]

Hey guys, my friend has a vz ss the cars in excellent condtion only done 70odd thousand, but it has this weird problem, randomly at any point in time it will stall doesnt matter if the air con is on or not, when it stalls the powertrain light comes on and has to be restarted again, it isnt a mechanical fault cause it isnt like it shudders it just cuts out, the radio turns on and off randomly and the other day the fog lamp dash light was flickering rapidly and the more he accelerated the brighter the light got. i really do get the impression its a electrical fault, we have taken it to a mechanic numerous timmes and they said that no faults are showing up on the system?
any ideas

[axemurderer101]

id be checking the voltage of the battery when these things are happening, the foglight lamp sounds like the alternator is not putting out a constant voltage