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Thanks to all for your valuable input. I finally got a chance to work on it after baling hay. I did not have access to an oscilloscope, so I used the ohm meter set to ac voltage to check the cam sensor output as recommended by haymaninva. The tach was not working for the first part of my test and later on it started working. So I was able to check it both ways. With no tach function, there was a steady ac voltage that did not vary with engine speed. Then after getting the engine fully warmed up, the tach started working and the ac voltage increased with engine speed as was recommended. So you guys were exactly right about the tired magnetic pickup. I had been on JDPARTS and listed the required parts for replacement, which agreed with those recommended by buickanddeere. I had removed the magnetic pickup long ago thinking I would be able to see something wrong, but could not. This time I took it apart. There is small center cover with the original part number that can be removed after some difficulty. After digging out a fair amount of hard sealer, I found a fine copper wire that was originally soldered to the ground terminal inside. It had continuity to the tach terminal, but no continuity to the ground terminal inside. The wire was so thin I had to use a magnifying glass to work on it. Eventually I got a jumper strand of wire soldered in to complete the circuit. Filled the space with silicon and resealed the center cap. The tach now works like a charm. Thanks again for your excellent advice. It saved the day. Mark
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