truck turns over won't start on 2000 Ford F-350 Super Duty

the code read out p0683 which is glow plug module 2 pcm communication circuit.Replaced both the glow plug module an air heater relay.one person say's it can b the valve cover gaskets?

1 answer 1 comment
Yes, the wiring to the injectors and glow plugs goes through the valve cover gaskets and may be defective, very common. So, remove the valve covers and carefully inspect that wiring. It will be pretty obvious if the wiring is defective, chafed or broken.
we check the gaskets with the meter and they r both good ,so we check from gaskets to glow plug module ,we got power ,so check 2 glow plug relay ,relay new so we check the wires to it .? is were do the little red an purple wires go to ,do they run to the pcm or fuse box?