Whenever I attempt to start I alway leave in the glow plug key switch position for a few seconds before engaging the starter. Normally in the glow plug position there is an yellow light that comes on. Today it won't start. The glow plug light only flickers on for a second but then goes off and seems to drain all power from the other starter lights. Never allowed to even engage starter after that. Battery is good. could it be the glow plug relay or controller? any ideas???
More likely you have bad battery connections. Do you have repair ends on the battery cables like this one.
Remove the ground cable where it attached to the frame or engine block and clean.
Replacing battery cables with new ones solves most problems.
If you have a multi meter and can do voltage drop tests then follow this DENSO procedure to find where the high resistance connection is.
Have battery tested. The test is free at most auto supply stores.
The GP's and their controls are not draining power. You have high resistance connections in the battery cables which are inhibiting current flow under high load conditions.
Best if you identify your tractor more completely as sometimes it makes a difference. 2WD gear, 4WD gear or 4WD HSD
Dave