Your earlier post said that the lamps were 0.3 amps so they should not blow any automotive fuse, is the relay in a cradle or just connected with fast-on / spade terminals? Can you disconnect 87 at the relay & see if the relay clicks when the switch is operated, do not put the car in reverse while it is faulty or you could do some damage.
Do you have any test gear, a test light and multimeter?
Graham