my '88 vn750 gave me fits a few years ago, dim lights at times, no neutral light at times, no speedo lights at times, gas gauge not working at times, finally got pissed off enough (after killing the bike at a red light, being in gear when i thought i was in neutral) to pull out the headlight. about 30 seconds into the repairs i saw a pretty big connector plug was not plugged in all the way. "click" and the headlight back in, problems were solved. check all your grounds, pull the battery cables off and clean 'em with a paste made of baking soda and water, flush well and let dry, put some dielectric grease back on 'em. next check the headlight bucket connectors and frame grounding cable. it sounds like a loose/corroded ground to me. my symptoms were about the same. good luck!
2003 VN1500 Nomad FI Bagger
2004 KLX400SR Dual Sport light adv bike
1969 CB750 K0 sand cast #1767
couple of nice GL650 Silver Wing Interstates, one with hack
2 and 4 stroke dirt bikes
other vintage stuff back in the corner