Which is relays or switch

[Duroman]

My glow plugs don't come on .I have a service engine light on, My scan tool tells me no glow plugs. Could it be the switch or the relays. What are the chances of either one being bad. How much time to replace either one? Does the switch come withe relays?

 

[2004LB7]

Switch? I'm not sure I understand what you are referring too. The relay is on the top of the engine and easy to get too. Follow the large red wire up to the relay.

Also, cali or federal LB7?