Hi All. I have a 1979 MK2 Ford Escort and the lisence plate lights on the rear bumper have stopped working. They've been out before but I've always managed to get them going, but this time nothing is working. I've put new bulbs in, unplugged the lighting component and checked plug connections, checked the fuse. Is there any advice on trouble shooting before I take it to the shop? Thanks. 

Do you have power at the sockets which connect to the light units?

Got it sorted. The grounded wire in the boot had been broken. Managed to reattach it without too much hassle. Thanks for your input escfalcap. Happy days and bright lights.