F350 Powerstroke GlowPlug relay issue

Have a problem with blowing out the glowplug relay on my 99 powerstroke. Replaced it last Thursday, and it is out again today. I know of one two others who have experienced this issue, they have resorted to starting with ether. Fine in a pinch, but not my long term choice of solutions. It is fairly evident that the control coil is getting fried, but the question is why? The replace ment coil was not a Ford part, but one from NAPA. Would like to know before I drop another $50-$70 on another solenoid.