Having done a bit of looking around It seems you should also check the grounding wire - this connects to the case using one of the screws that hold the cover on (Top right if the pictures I've seen are correct), if this wire is not connecting properly then you can get odd faults...
Thank you so much for your help everyone, it really is very much appreciated, @Tubbyengineer I followed your advice about the grounding wire & the mod now works a treat, once again thanks so much for your time, advice & help [emoji2]