my ford 641 tractor uses a charging indicator light instead of an ammeter, do i have to use an ammeter guage? my tractor has 3 guages, temp, oil pressure,and fuel.

I forgot to mention that if the Warning Lamp comes 'ON' it means your Generator or Alternator isn't charging the battery, likely due to improper fan belt tension, or, your wiring isn't right. You need to have a fan belt tensioning device attached to whatever system you are using otherwise you will never charge the battery. OEM 6-Volt/Positive Ground Generator had an attached bracket; 12-Volt conversions have been done by many owners but not all Alternators come with a tensioning bracket. In addition to charging the battery, proper fan belt tension is also needed to maintain the cooling of the fan to prevent overheating of radiator.

All FORD's on the NAA/500/600/700/800/900 Series used the same basic dash panel setup. Gauges are AMMETER on Left, TEMPERATURE center, OIL PRESSURE Right, and the PROOFMETER at top center, the large faced one. There was NO FUEL GAUGE. Do you have your Owner/Operator's Manual?

I like amp meters. The electric shops like volt meters.
If you run stuff downstream of an amp meter, and it quits, the stuff downstream quits.
However the amp meters on the early Ford cars were different. The amp meter had a heavy wyre run thru a loop at the back. No break in the wyre. Maybe that type is still available somewhere.

Light comes on to indicate a fault. Generally if the light is off while running, you have no problem.
You have a problem?