If you are okay with replacing the gauge, here is a Stovebolt Tech Tip that shows you how to replace your current AMP gauge with a modern Voltage gauge and disguise it as an original gauge in your existing gauge cluster.
http://www.stovebolt.com/techtips/electrical/voltmeter/Does your alternator have one large post and a two prong plug? If so, the larger wire of the plug can be used to feed your gauge cluster through the ignition switch. You would be better off with the 55-65 AMP alternator. The smaller wire feeds an alternator warning light. If it is truly a one wire alternator find a local rebuild shop. My local guy said he can convert a wire to 3 wire or 3 wire to one wire for about $20.
I just converted from a generator to an alternator last week. I also added a 50 Amp Auto Reset Circuit Breaker inline before my instrument cluster to protect the AMP gauge. The information I found is the original AMP gauge is rated at 50 amps. My Alternator has a potential 65 amp output but that should never happen, but the breaker will protect things if it does. RESULTS: steady 14.43 volts/charging at battery, steady bright headlights. The only thing I am thinking about doing is pulling the alternator back off and painting it black to camouflage the fact I have an alternator. That bright silver case stands out like a sore thumb.
