Bob M may have it right, electrical noise on an old point type ignition system will make a DVM read high. I saw that last summer while checking battery voltage on my Moline Big Mo 400 with stock point type ignition and 3 wire delco.
I checked charging voltage at the battery posts and was getting a very high and eratic reading with a digital volt meter, 17 +. That did not seem possible, as the ammeter reading was only about 5 amps at high rpm.I got my little chepo 50 amp battery load tester with the big analog voltmeter and connected it to the battery posts. It read a correct 14.5 volts. With the engine shut down, the DVM read the correct 12.6 volts, but aparently could not handle the noisy voltage signal from a running spark ignition tractor.
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Today's Featured Article - Third Brush Generators - by Chris Pratt. While I love straightening sheet metal, cleaning, and painting old tractors, I use every excuse to avoid working on the on the electrics. I find the whole process sheer mystery. I have picked up and attempted to read every auto and farm electrics book with no improvement in the situation. They all seem to start with a chapter entitled "Theory of Electricity". After a few paragraphs I usually close the book and go back to banging out dents. A good friend and I were recently discussing our tractor electrical systems when he stated "I figure it all comes back to applying Ohms Law". At this point
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