In Reply to: Generator posted by Theo Morris on August 28, 2018 at 12:19:22:
Kevins' explanation is right on.
WHy did you replace the ammeter? Was the battery running down causing you to think the generator/cutout was bad? Or were you worried because the needle didn't move very much? THey hardly move even at full throttle if the battery is fully charged. If you keep it hooked to a Battery Tender it may not move at all. Most of the Fords in good tune start in a revolution or two (sometimes less) in warm weather so there is little drain on the battery when starting. Drain to the coil is minimal and would be almost undetectable on the vehicle ammeter. On a quality tester reading in tenths, no problem.
The ammeter ONLY reads amps. Your vehicle ammeter is connected inline (series) in the hot lead to the battery. Voltage can be tested across the battery terminals. 6.2V to a little over seven (over 7+ if the battery is older and a little sulphated.) depending on level of battery charge.
The original and replacement gauges have wide needles and numbers close together, so interpolation (guessing) is necessary. Simply put the ammeter provides gross readings, You won't be able to tell if its charging the 1-2 amps to make up for the drain to the coil, especially if the commutator is a little worn and the brushes are bouncing a little.
Easy check to see if it charging using the ammeter. Run the battery down a little by engaging the starter with the key and gas off. THen start it and watch the gauge. It should go up to around the 6-8 numbers and maybe wiggle a little depending on the condition of the generator with about half or better throttle and return to zero pretty quickly as the battery returns to full charge.
You can also check for current at the battery posts with a test light, but that will only tell you that you are getting voltage.