use a normal test light, clamp the wire off of the top to the positive terminal of the battery. disconnect the wires going to the glow plugs and touch the tip to the top of the plug. if the light comes on then plug is good, if not it is bad, clean all connections and use electrical grease sparingly on each connection. A bad connection will cause the same symptoms as bad glow plugs, sounds to me like you have bad glow plugs. if you have the electric pump mounted in line with the mechanical pump that could also cause problems later down the road so I would mount the electric pump on the frame rail after the fsv and use relays to trigger it on or use the mechanical pump, but not both