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.