We had the opposite problem on our B3. The aircraft would occasionally refuse to start when the start switch was selected.
For its entire life, it had this problem and had found itself grounded in various remote locations. Switches, FADECS, and many other boxes had been swapped chasing the source.
Some pilots swore that hitting the rotor brake lever with a hammer fixed it!
It struck me after I ferried it to a local dam to do belly tank bombing with CASA. They wanted their FOI's rated on the tank.
We strapped in for the training and went for a start and got nothing. Very embarrassing. No amount of flicking switches, or tapping/bashing the rotor brake got it going.
They ran out of time and went home and I sat in the paddock waiting for the engineer to arrive.
The engineer was sick of this machine as he had been chasing this problem for years.
I have a background in electronic engineering so I was keen to assist him as he had all the schematics with him. We traced the wires and worked out that there was intermittent ground on the rotor brake microswitch.
It was intermittent in a way that if anyone was in the aircraft, standing on the skids or even leaning on the fuselage we would lose the ground and go open circuit.
It took us forever to locate the ground terminal block under the airframe. We had removed all the cowing trying to locate it as the schematics and maintenance manual were very vague in its location. I eventually found it and located the wire by its label.
I could see straight away that the pin was not fully seated into the block. I gave it a push and felt it snap into place. Most likely it had never been correct since it left the factory. It was near enough that when the airframe flexed just right it would go open or close circuit. It was just pure luck that after you landed it was in position that it would start again.
We checked all the other terminals and found no issues so closed the machine up and it started the first time and never had a a problem again.
The only time the engineer has bought beers for the pilot - it's always the other way round!
Oh and then there was this time on a hospital rooftop when an EC145 after the first engine started, refused to start its second engine......
