classic fuel pump relay not switching

[bones]

Hi.I have a 1995 reg V8 classic which means the wiring is different in many places compared to other classics. The fuel pump relay isn't switching. The power input (purple and white wire) has constant battery voltage OK. The switching input wire (white and green) gets battery voltage with ignition on and goes to the other side (blue and purple wire) OK. But the relay doesn't switch so no power going to the output side - 2 white and orange wires and the white and purple wire that powers the fuel pump. So no starting. I take it this means the blue and purple switching wire isn't getting earthed to make the relay switch. I believe it goes to the Engine Control Module. How can I test this. Any suggestions. The relay works on bench testing but I did try a new one anyway but still no joy.