the above has nothing to do with the glow plug relay but relates to the wires between the ECU and the injection pump (fuel cut solenoid, which was what your question was about?).
Glow plugs, EC section . Pin 111 of the ECU is the one which "grounds" the glow plugs relay. You could cut and add a manual switch to "ground" this relay and activate the glow plugs" only if and when you want.
And don't ground the ECU pin, as this will NOT work.
It is the relay pin 2 which needs to be grounded through your manual switch. But what if you forget ?? I would NOT do this if I were you.
If you really want to modify, apply the "australian timer mod". It has been widely tested, and for a long time.
But why would you do this ? I live in the south of France, lived in south of Spain too, and never modified the start sequence of my glow plugs for 23 years on my Patrol. Same stock head. Nobody found any good reason to do this, or did this, in my country, from North to South..
