Sub stopped working need help troubleshooting

[jazzamead]

Hey guys recently my sub kept cutting in and out I assumed it because the amp wasn’t powerful enough for the sub. Eventually it cut out completely I went and checked the fuse and it had melted the housing and burnt the cable. Since then I’ve purchased a new 800w jvc amp and some 4 gage wiring but I still can’t get it to work. I have an rca convertor running off the rear left speaker could it be the problem? Haven’t had an issue with it before but I’ve checked all the wiring and the sub had power and remote wire is fine also when you plug in the audio cables the sub makes a thumping noise so I don’t think the sub or amp are the problem.

Any help would be greatly appreciated cheers boys