Thick red wire heating up

Hi all, I have a 1991, GTI cabriolet and seem to have this red wire getting very hot, I wanted to know where this wire goes from the back of the fuse box. It's the one in the back, not the front one. Also why would it be getting very hot. Any info much appreciated

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see:
https://www.cabby-info.com/electrical.htm

Then page 10.
https://www.cabby-info.com/Files/ElectricalSystem.pdf

https://a2resource.com/electrical/CE1.html

Hi all, and thanks very much Briano1234 again for all your help, it was the spade connector that the wires goes into breaking up sorted it out and now it doesn't heat up as it did. Again thank for your help.