In Reply to: Ammeter polarity posted by Charlie Rohlfing on September 12, 2017 at 16:51:06:
We will assume you have a newer aftermarket style ammeter with the two screw terminals by your question. As stated, if readings are bassackwards -that is, negative readings when running, the wires simply just need to be reversed on the gauge terminals. No harm will occur if not right -no 'polarity' is required. The original 8N wiring utilized the AUTO-LITE Voltage Regulator, as shown in the picture below. FORD TRACTOR first used the -20/+20 AMMETER with screw terminals only on the first 4000 early 9N tractors, then released the "LOOP-STYLE" induction ammeter also shown in the picture below which now had the -30/+30 scale. Here is the LINK to JMOR's Wiring Pictograms as well to help better visualize the set up. Also, the I&T F-04 Manual, '39-'53 MPC, and the 8N Operator's Manual all have the wiring schematics complete with the original color-coded harness wires labeled. If you do not have the original cloth covered/color coded wiring, or a DC newer, exact-as-original wiring harness, do not assume wire colors are correct. The best procedure is to get the wiring schematic and do your own wire tracing and continuity checking to be certain all is right with the world before applying power and risk letting the smoke out of something if it is not correct.
EARLY 8N WIRING, photo courtesy of Steve Dabrowski: