Early preglow relays of 5-cylinder diesel engines (250D) built up to 1988 do not have an integrated electronic self-regulating fuse, but a classic strip fuse.
If you are not sure which version of the preglow relay is installed in your vehicle, remove the protective cap of the preglow relay: look at the pre-glow fuse there.
Since the engine only starts badly or not at all if the fuse fails, we recommend always carrying a preglow fuse in the vehicle.
