I have to assume these are the old series type, if so if any one of them is badly connected none will work.
Do you get the heater light come on on the dash when ignition in correct position?
If no check for continuity of the ballast resistor on the baulkhead. If that appears to be OK.......
If you have a meter you should be able to get a resistance reading between the earth wire connected to the plug at the front end of engine and the wire in from the ballast resistor at the back end.