what is causing my glow plug light to flash constantly on my 02 transit ?

i had a split in my intercooler but the van seemed to be still boosting quite well, i have now replaced the intercooler and sensor for a second hand unit and now my glow plug light flashes and there is no power, i have tried to change the sensor for my origional one but the fault is still there. Runs perfect but no power and struggle to get upto 50mph. Please help!!!