I bought an older 753 F-series. So far I installed a new cylinder head, went through valve body and rebuilt the drive motors;however, I'm still at a loss why my glow plugs won't engage. On my model, you turn the key to the left to energize the glow plug relay by the air cleaner. The machine doeshave the early BOSS set-up. Looking at the schematic I see that the power coming from the ignition switch (when turning left) goes to the glow plug relay but also it feeds into the BOSS controller. Would the BOSS controller some how control and not allow the power to go to the glow plug relay if not needed? I have continuity at the terminal on the switch and the glow plug relay but when I put 12 volts to the terminal at the switch, I have no voltage at the glow plug relay. Any thoughts or suggestions?