The power wire has no other fue than the 80A one; meaning its straight battery hot all the time.
Next to the fuse are two connectors on the relay. The larger one will have six wires. One to each glow plug. With an ohm meter check each wire to ground. Use the lowest scale as the value is less than one ohm if good.
Most likely you have a bad relay as its unlikely that all the plugs went at once. As plugs burn out the glow light will flash after starting.