Nothing makes a mechanic's shoulders sag faster than a customer who has a machine with intermittent mechanical problems: "Sometimes the feederhouse won't turn on when I push the button." "Two or three times a day the transmission jumps a gear." "The planter's marker arm only works about half the time."
The customer wants his malfunctioning machine fixed. But a mechanic can't fix something if it's not malfunctioning at the time he's near the machine. Modern machines, with computers that record system malfunctions for later recall, sometimes provide mechanics hints of what the problem is, but the best way to diagnose a malfunctioning machine is still to be there and see, hear and feel what's going wrong while it's going wrong.
If you have a machine with come-and-go mechanical problems, ask yourself each time the machine mysteriously malfunctions, "What changed?" Is there a pattern to the problem? Does it happen only when turning at the end of the field, raising to go across waterways, maybe only when going uphill or downhill? Does the problem occur in heavy crop or only in thin areas of crop? Dumb as it may sound, were you sitting differently in the seat, were you talking on the cell phone or FM radio, or what time of day was it?
All those small things can help a mechanic figure out the problem. "Dumb things" can make a big difference--some cell phones and FM radios cause interference with electrical systems. Or, there are certain times of year at certain times of day when the sun's angle in the sky, sunspot activity and other astronomical phenomena can make GPS and radio-based systems go freaky. Weird circumstances can make machines do weird things.
I once spent several years trying to diagnose a mysterious glitch in a combine that only occurred in one narrow band in one specific field. Whenever that combine was in that area of that field, the slow shaft speed warning lights would intermittently go on and off--mostly on. There were no mechanical malfunctions in the machine, and the farmer and I eventually agreed that specific area of the field was haunted. Years later I ran across an aeronautical map that showed the zones and paths of radar for the airport in a large city near that field. Lo and behold, the radar beam that guides commercial airplanes to the main runway at that airport passes directly over the area of the farmer's field where the combine's sensors always went goofy.
Was that the cause of the malfunction? Could a high-intensity radar or radio signal trigger malfunctions in a combine's electrical system? I'll never know for sure. But it taught me to always think outside the proverbial box when it comes to diagnosing intermittent, odd, or unexplainable malfunctions in machinery.