This is a NEW OLD REPLACEMENT STOCK (NORS) 4-wire turn signal relay for your 1966. You will find this mounted on the driver side fender wall just below the master cylinder. Some cars use this relay and others use the 3-wire version. If yours uses the 4-wire version, this is the one you need. The wire colors on this relay are different than the original which had blue, yellow, white and brown wires), but it still works great exactly as it should. The second photo shows an original 4-wire turn signal relay.
Please send back your old relay so that I can re-build it to keep another 66 Lincoln on the road.