Glow plug fuse keep blowing - PeachParts Jun 04, 2010Having a problem with my 1985 300D Turbo. The glow plug fuse kept blowing so my mechacic said it was the glow plug control box. I replaced the glow plug control box, but it still keeps blowing. Thought it might be the glow plug wiring harness but can't find one to replace it with anywhere. Before I build one does anyone have any ideas.87 300D blowing glow plug fuse - Page 2Mar 14, 2016Glow plug fuse/wiring question.Jun 12, 2010See more results Mercedes W123 Glow Plug Fuse and Fuse Box, Early Style The glow plug systems on early Diesel W123 cars, mostly 1980 and earlier, have a glow plug relay that is underneath the dash within the cabin of the car. In these systems the fuse for the glow plug is located within a separate fuse box attached to the firewall of the car.