312 lwb heater light advice

[m-m]

I have seen other posts similar ( sorry if I am repeating one )
My 312 van ( 1997 ) has just started to put the glow plug dash light back on after it starts. It will start as normal, the light will go out then instantly comes back on for about 1 mile then stays off untill you re start again.
From other posts I suspect the timeing relay going faulty. What do you think ?
If it is the relay is it in the black box by the battery ?

 

[m-m]

Anyone got any idea's to help with this ?

 

[Bigtee]

You may have a faulty glow plug try removing them see if they glow & check timer opperation some do work with the coolant temp sensor so if v cold gives more power= more heat to plugs.