Thanks for reply tried a complete reset cv8=8 no joy made sure decoder fully home on the pins still no joy tried the decoder in my other 2 121's got the same issue no main headlight im sure your right about the bit in cv's that need to be turned on its finding the correct cv and the bit dont want to mess about too much with the cv's and completely mess things up was thing of returning the decoder to marks models where it was purchased and exchanging for another see if I get the same issue