Just hard solder the wires to the light board tracks, ford used galvanised steel for the light tracks, which is bad news for conductivity lecky wise, the micro arcing that occurs on the pins then burns off the galvanise letting the pins/connectors rust.
Even when sorted always run a seperate earth, to a decent point, takes all the trouble away.
I drill a 3mm hole in earth track then insert a tinned wire and solder on, it will not come off ever if done correctly then other end put a terminal etc as needed and earth down.
You can use the same technique to join the loom to the light board tracks, could also do the brake/fog light mod whilst there so fogs come on with brake lights, via some rectifier diodes, all easy to do cost around 20-30 pence, 100% LEGAL and MOT passable, do this on all my cars, have done for 20+ years, makes a huge amount of difference having fogs light up with brakes, but still work on their own as fogs without affecting brake lights.
tabetha