On the right hand side of your picture, you call out an ammeter; is that correct?, or is it actually a voltmeter? Seems to me that by '69, it should be a voltmeter; I can't remember for certain. If it is indeed an ammeter, DO NOT GROUND IT; you will be making a dead short, and may start a fire, or at least kill your battery and alternator. A voltmeter, on the other hand, reads from pos. to grd., and should have a post marked that way.