1972 Norton Commando, Alternator ?

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May 27, 2008
My alternator has not been recharging my battery, but I don't know any good ways to trouble shoot to check and see if the alternator has gone bad or if it's a wiring issue.

What are some good ways on a 1972 Norton Commando, to trouble shoot the alternator?
Factory test

The factory test is to disconnect the alternator and connect a 1 ohm resistor to the alternator wires. Use a voltmeter on the AC scale and note the readings, you should have at least 9 volts AC and the following the following current when measuring the alternator output:

up to S/N 211279 from S/N 211280

1000 rpm 2.5A 3.0A
2000 rpm 6.7A 6.8A
3000 rpm 8.5A 9.4A
4000 rpm 9.3A 10.0A
5000 rpm 9.8A 10.4A

Be sure to use a resistor with a high enough wattage rating. At full output the alternator will produce 120 watts. I've used a 10 watt, 1 ohm resistor with no problem. I think I got the 10 watt resistor at Radio Schack. Hook everything up, resistor and meter, then start the engine. Once you get the reading, shut it down. Continual running will burn up the resistor.
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