I was talking to a Phoenix Ratsuner about dome lights for 620's(any truck for that matter).I told him about this Ford piece and I told him I'd post this.This also comes on a shit-pot of Ford trucks,so boneyard finds should be easy.
http://www.ebay.com/itm/NICE-Original-OEM-73-96-Ford-Lincoln-Mercury-Overhead-Dome-Map-Light-CHROME-/171390670577?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A1990%7CModel%3AF-150&hash=item27e7ae16f1&vxp=mtr