My 1980 Trillium
4500 has an extra light
bulb (1156) on the right side to the left of the 1157 bulb. Does any one know what the pupose of this would be. I thought at first it was a backup light
but I don't think the 7 way plug includes that. Then I thought it was for the licence plate running light
but that is always located on the left tail light with the plate. The bulb seems fine but I am not understanding the purpose of this extra light inside the right tail light.