My glow plug indicator light (and glow plug function) no longer come on when I turn on the ignition. I checked the glow plug relay and that appears to operate fine, and the glow plugs test out fine. I suspect that the glow plug timer (LG4056/LS TRG750 - 4 pin glow timer) may be the problem, but I don't want to spend the money buying parts unless I'm sure it's the timer that's failed - how do you test the timer? No indicator as to which lead is which (three connectors on one row and one on the second row) - Tractor is a DTC300; but I think the circuits are the same on most tractors of that size.