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the way to tell is to use a voltmeter and check the voltage across the battery when the car is running should have 14 volts at the battery
If you do not have a voltmeter you can remove the alternator and have a parts store check the alternator and load test the battery
by your description it sounds like you have a alternator that is going bad
without having a voltmeter, isn't there a way to tell, like I said, when the rpms are increased, the lights get brighter, doesn't that just by it self indicate whether or not it is the battery or if it is the alternator at least for the most part?
do you know of any suzuki sj410 owners clubs, and/or where I can get parts to restore my sj?
sorry i do not. but I would google it I am sure there is something somewhere on the internet.
your welcome and have a great day
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thanks for the accept