When I turn on the left or right blinker, the tail light has a dim blink also. Checked the main ground, it's clean and tight. Could it be the flasher? Any ideas? The bike is a 2007 900 Vulcan Classic LT
No not likely.
It could be the battery or the charging system......OR if the blink is faint, it could be "normal".
Have you checked/cleaned the socket for the tail light......and the connectors for same ??
I can't check mine as a comparison 'cause I've changed my taillight bulb.