My 300D has eaten three 80A glow plug fuses today. I had already replaced the fuse about a year ago when it blew, after having replaced it a year before that. Today it's become much more keen to burn them up so something is clearly wrong.
Per my search of other people's problems with this I have checked the harness for any wires sticking out and contacting the block/head/intake/fuel lines ... I just cannot see anything out of place. Five of the glow plugs measure .8 ohms and one measures .7. I am getting 12.06 volts at the fuse with key on. I cycled it a few times while testing and it did not blow, but the hot end of the fuse gets REALLY hot, burned my finger. It didn't get hot with the harness unplugged. I'm not sure if that's typical or a sign that the problem is in the harness. After a couple test cycles with the harness on, letting it cool between, it blew again and now I'm out of fuses.
Any ideas what other tests I should do? Could it still be the controller causing the issue, maybe I should try replacing it? Under normal conditions, does the fuse get really hot to touch?

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)