By the color codes, it looks like the junction point for the 7 wire truck connection cable. It looks like someone made a home made plate out of it. While I have not seen a 1984 Sunline and how they did the 7 wire junction box, they normally do not create it out in the open subjected to the elements.
If you can take some side pics, I may be able to back into what they did and the fuse purpose. There are generally 2 fuses or forms of fused protection.
1. A fuse, many times a 30 amp fuse, is in the truck charging line. This allows the truck to charge the battery while towing and the fuse helps protect the truck in the event of a short.
2. The next area which can be a fuse or a circuit breaker, is between the battery and the onboard power converter. This protects the battery, the wiring during power draw from the battery and to the battery and for short circuit protection.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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