Tech Alert: On the 1981 to 1983 XV750s and XV920s, there is a problem with the ground cable from the battery to chassis;

The ground ( - ) cable is secured to one of the bolts in the bottom of the battery tray that holds it to "Bracket 3",  or the triangular aluminum bracket that holds the exhaust, and rear foot pegs on the right side of the bike (as you're sitting on it). (see image below)

Bracket 3 (4X7-27443-00-00)
The yellow highlighted are shows the rear
battery tray mounting boss. The ground
cable from the battery connects on the
bottom of that bolt UNDER the
battery tray inside the bracket.

Unfortunately, that connection will deteriorate over time due to the aluminum and alloy metal of the cable connection and the bolt, exposure to water and constant current running through it. The aluminum breaks down to a white powdery substance and the ground is no longer true.

The remedy is to drill and tap a small hole into the side of the steel frame behind the battery, and add a separate bolt for the ground. The cable that came on the bike will be long enough to reach, and by rerouting it there you get a better ground.

Some symptoms of a bad ground can include;

The solenoid just clicks rapidly and doesn't start the bike. Sometimes this can be accompanied by a flickering tail light or turn signals as the system tries to ground through those lesser connections. 

The tail light comes on with the key, but dimmer tan usual, and the starter turns over slowly until the solenoid just clicks and the bike won't start.

The battery doesn't charge efficiently, so if you start it several times without running fast for a few minutes the battery may drain to where the starter will not turn.

There are other scenarios that may tip you to a bad ground, but these are the top few.

After repairing a ground on a Virago that hasn't been right for some time, you may notice that there seems to be some corrosion on the positive terminal. Don't ignore it. Clean the terminal thoroughly or you may be back running diagnostics again in a short time.