Usually, a fast flash indicates a burnt out bulb. However, when you mentioned the back up lights come on dim, that tells me there is a ground problem. What is happening is the ground for the signal is lost. Electric takes the easiest way out and in this case it finds a ground through the back up lights. Check for broken ground staps, broken or damaged wires.
Let me know what you find.
Thursday, March 11th, 2021 AT 7:15 PM