TC25 Glow Plug Operation

   / TC25 Glow Plug Operation #11  
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.

From 1520 Service Manual
1520 Glow Plug Wiring.jpg

From T1520 Service Manual
T1520 Glow Plug Wiring.jpg

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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   / TC25 Glow Plug Operation
  • Thread Starter
I ended up installing a 20.00 ignition switch with a glow plug warming position to the left of Off. This is like my dad's IH 234. Turn the key to the left for a few seconds then start. Works great.