Take a good look at the replaced Strip Fuse to see if it is cracked.

Also don't discount that there is an issue with the 28 year old Ignition Switch. If the Ignition Switch is not sending the Juice to the Glow Plug Relay the Glow Plugs will also not get Electricity.

Also you can see a Flat Copper Wire when you can see the Strip Fuse on the Glow Plug. Make sure the screws are tight on the Wire and the Strip fuse.

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84 300D, 82 Volvo 244Gl Diesel