[maxwedge]

Number one is usually a carb issue assuming no vacuum leaks, high test fuel, proper tune up specs. 2 could be the regulator, a voltmeter should be used to check alt output, 3 disconnect the gae wire at the tank look at the gage, then ground that wire, if the gage reads full then empty the dash gage is good. You should have a shop manual if you want to be able to properly work on this.