I had this random thought one day...why did I have to replace one of my tail light bulbs with a 3157 wedge bulb when the owners manual calls for an 1157?

Finally I had to see for myself, and sure enough...the driver side tail light bulb is an 1157, while the passenger side tail light bulb is a 3157 wedge.

Any takers on why Ford may have fu-barred???