im in desperate need of someone who really really knows the engine management side if a Silvertop escort

im really at a loss and bloody confused

the injectors wont fire , there is a permanent 12v at them all when ignition is on , which is correct . if I use a noid light they are getting a signal ,
if I put a earth to them they will fire
I can only assume that the negative which Is switched is poor

I have a spark so I assume crank position sensor is good
I have checked the 3 earths at the ecu and all good
I have a string 12,4v on the live side

im stumped. truly stumped. , if anyone knows a way forward please let me know , happy to pay for a phone call. , just stumped

thanks anyone

1992 xr3i
non PATS