I am pretty certain that the timer relays shown near the beginning of this thread by tmeric7 are only what their labels indicate, "lamp timers", and are not glow plug timers. These relays only control the ON time of the glow plug indicator light and do not control the actual glow plugs. The glow plugs are ON only while, and as long as, the key is held in the glow plug position. This definitely applies to my New Holland 1520 from testing, and is supported by manufacturer wiring diagrams. My T1520 operates the same way except that in place of having the lamp timer, the glow plug indicator light time is controlled by the safety controller, but the glow plugs are still ON whenever the key is in the glow plug position. The New Holland 1520 and T1520 are very similar to the TC25, 29, 33, & TC30 (all are Shibaura) so I would expect the basic wiring and operation to also be similar.
EDIT: I have learned that at least some of the TC models (except maybe the TC30) do used the lamp timer relay to also control a relay which energizes the glow plugs while the lamp timer is on. My 1520 & T1520 do not have that relay.
From 1520 Service Manual
From T1520 Service Manual
There is no glow plug relay, they are direct wired from the battery through either a fusible link or a 40 amp fuse (depending on model) to the ignition switch to the glow plugs.
I have added this information because I see a lot of confusion about how New Holland uses these NGK lamp timers on these Shibaura compact tractors.
EDIT: I have learned that at least some of the TC models (except maybe the TC30) do used the lamp timer relay to also control a relay which energizes the glow plugs while the lamp timer is on. My 1520 & T1520 do not have that relay.
From 1520 Service Manual
From T1520 Service Manual
There is no glow plug relay, they are direct wired from the battery through either a fusible link or a 40 amp fuse (depending on model) to the ignition switch to the glow plugs.
I have added this information because I see a lot of confusion about how New Holland uses these NGK lamp timers on these Shibaura compact tractors.
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