Bulb(s) on but won't flash... See my Cave, Sneak Path
Check all rear sockets. You need to remove bulbs from the shell/lenses. Turn on park off or turn off park on then only 1 filament is on. Both on then has iffy ground in that socket.
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)