There commonly is a B/R lead with 12 V to the sensor. You can check it at the sensor connector (with the bike on). If it's not 12 V, one or more contacts on the connector between the main and front harnesses are probably failing. That's fairly common on bikes of your vintage. There's probably a big connector with a sheath inside the left front cowl. But the location and details can vary and I don't have your manual. Look for the B/R and P leads. There's also a B/W ground lead but you'd have bigger problems if it was bad. You can also check at the cluster connector.