Answer by
Doug77 (1433)
Older Ford trucks used a sealed halogen bulb and housing assembly, most likely part number H4656.
Newer models (1988-ish) started using a compact bulb that was easier to replace. The most common part number is H9004 but, some use the H9006.
It's best to remove the old one and look for the 'H' number to be sure.
