Number plate lights

[PhilRenault79]

I have a 71elan plus 2. Had a new wiring loom installed by Spyder cars with fuse box in the glove box.
I come to wire up my number plate light and all that happens is I blow a fuse in the glove box, lose the near side front & rear side light, and have no number plate lights. Do I need to wire an inline fuse in?
Was told to connect all the black wires to the earth coming off the loom and the same for the red wires but as I say nothing happens accept blowing a fuse.
So I’ve come to a dead end and need some advise please help