Hello E, I am not familiar with your machine at all. But Have some questions which might help. You have so many symptoms and each one is not normally found all together like this. The fact you saw 5V at the start terminal makes me wonder if what you are calling starter relay is not the safety interlock relay for the starter which can cause that.? The fact you saw 2V makes me wonder weather the back EMF diode is leaking and they are sometimes at the relay, or fuse box with the safety interlock diodes or in the monitor.? When you say it some times does not turn over hard that is low battery voltage and nothing to do with starter or relay. Another symptom you are describing is the clicking. Now that can be two things. One is low battery voltage. The other is low voltage being applied to what you are calling the excite terminal. The way it works normally is the plunger in the starter solenoid gets draw in pulling the Bendix into the ring gear, and at the end of the stroke the contacts will close powering the starter. But occasionally the pinion will not go into the ring gear and in that situation the excite terminal has to be provided with more than normal current. As the plunger is draw in it has to compress a heavy spring behind the Bendix which is not normally compressed. When it gets to the end of its stroke power is applied to the motor and as it begins to turn the compressed spring behind the Bendix slams the pinion into mess of the ring gear. So low voltage at that terminal which you have measured would severely limit the pulling power of the plunger and they just click like you have described. The plunger does not get to the end of the solenoid to engage the motor. Regards