[Darren69]

You could, if you have enough free hands measure the voltage from the starter motor connection or the one that goes to it from the solenoid when you press the button. I think its not getting enough juice due to faulty solenoid or poor connection on the input side from the button (the plug that goes in the back of the solenoid connected to the starter button.) The starter button could also be at fault if it has poor connections.