There is a small light under my rear bumper, disconnected. What is it for, and what circuit should it go on? It appears to be original equipment.

thanks.

 

Not real sure but I think it's for the license plate for a truck with stepside bed, mine has it also and it's 8 ft styleside bed.

 

I know that years back at least around here, rear bumpers were not standard equipment. There were rows of brand new trucks without them. There had to be some other place to mount and illuminate the license plate though. That may be what your light was for. The 79' F-150 stepside I used to have was like that too.

 

I've got a license plate light, and this light has FORD logo stamped on it. It is pointing down at the right hand side of bumper, mounted to underside of bumper.

 

Sycostang hit the nail on the head with this one!
Ford trucks came from the factory without a rear bumper or a spare tire unless the customer ordered them.
The ones without a bumper had a light and a license plate frame bolted to the left side of the underside of the bed. If I remember correct you had to remove the frame if you were to install a bumper. Most people left the light in place, they just disconnected it and ran the wire to the new lights in the bumper.
About 15 years ago I bought a brand new take-off bed from an old man who replaced the bed on his new F350 with a utility bed. He had the bed and bumper in his barn claiming the bumper was the factory Ford original. Well, the bed was perfect but the bumper was aftermarket. The bed had the little license plate light up underneath to confirm it. I politely told him I will buy the bed for his asking price of $1000, however I'm not interested in the aftermarket (FEY) bumper, only a factory original and pointed out the little light to confirm the aftermarket bumper.
He turned bright red and yelled that he paid the dealer $300 for that Ford bumper and if I don't want the bumper with the bed to "GET THE F OFF HIS PROPERTY"
His son stopped me in the driveway and apologized for his father. I bought the bed for $1000
Steve G.

 

Thanks for the answer guys. Guess it will stay right where it is.

 

My '85 F150 has that tag light as well. Come to think of it it had an aftermarket bumper when I bought it. Mystery solved!