I had a car that failed to charge it wasn't obvious at all but the alternator ground to block it looked fine but it was dirty, it caused it to not charge. you likely have a blue wire connected to the block near the alternator,, check that one. I suspect yours may be dirty where it connects to the block.. if you changed the alternator you could have unhooked it, then transposed the wire to your new alternator, but failed to unhook where it is connected to the engine or ground point.. it is necessary for charging. also check that th eblock is actually connected to the body look for a ground strap that grounds body to engine.
hey if you add an extra ground to the alternator, to the body or to the engine or to the battery it wont hurt anything,, a jumper cable laid in parallel is an easy quick check just to confirm alternator or block grounds are ok.. better to clean it but if you can strap a ground across just using a jumper cable as a temporary fix as a test, and see a difference,, then you are onto something.
if you heat copper or brass and quench it it becomes soft, if you heat it and cool it slowly that makes it more springy, you don't need a lot of heat and you can change the metallurgy so you can re harden it to restore spring tension but it may be close to plastics. probably best to do a neat splice and put a new terminal on it.
often things lik efuse terminals, the springy holder things, they can get hot, loose tension and then its both loose and dirty. I know women like that. lol but your fuses you don't want loose OR dirty ;-) as you install the fuses after cleaning press on them and compare, do you have weakened springs? are they not pressing well against the tips of the fuses? are all the fuse tips clean? are they falling away from the porcelain part? they are easy to break.
if you need ot repair a wire,
to do a neat splice,, clip and strip the wires, make sure they are clean. do a western union splice
look here:
https://en.wikipedia.org/wiki/Western_Union_splice
put heat shrink not black tape on the wire then splice then solder, then pull the heat shrink overtop and use a lighter to shrink it, don't use black tape unless you absolutely need to. often what I will do is do a real nice solder joint then realize I forgot to slip on my heat shrink,,, so I can cut it apart, start over and repeat it then.. I must love soldering. Put the heat shrink on FIRST!
any connection I find that is properly heat shrinked is trustworthy and ok, i know I did that.. but any blacked taped connection is not mine and is suspect, so I find those I unwrap to see. often some dimwit twisted the wires wrapped it with tape and said good enough .. that crappy workmanship will often come back to haunt you so just bever do that unless it is a temporary test or similar. always solder !
never put heat shrink over any splice that is not soldered.. you'll hide the cause of a problem.
that splice will have no resistance and no measurable voltage drop.. if you spot wire that when you strip and it it it is green or dirty looking change as much of that wire as possible without it becoming a huge project. if some previous owner made connections wrapped in black tape undo them, if they seemed to not solder or make a lousy joint then look for other places they did the same.
if you always make good splices you'll never have any issue with bad ones that you did.
some dot know how to solder, keep the tip clean, load it with solder, take a wet sponge and wipe the tip and make sure the tip always is wet with solder, if the tip wont take solder , stop, clean the tip re coat it with solder.
often people will hold their solder iron on too long, it should heat and be done quickly if the tip is dirty you'll have to struggle and you'll heat to long.
if you want to contain the heat to the point you are working on try clamping small vice grips or an alligator clip on the wire to suck heat away like a heatsink.
just so you aren't melting the insulation an inch from where you are soldering.
the battery cables buy new ones , don.t mess around , idf they re old they are done they aren't expensive or proprietary.
you don't need porsche brand battery cables any more than you need porsche air in your Porshe tires. Don't get sucked into that proprietary nonsense. its a hunk of wire with a standardized battery post. often better quality wire also has more fine strands, maybe ask where you buy your batteries. If you can find ones not made in china you are lucky.
I wouldn't take this to a Porsche specific dealer or mechanic What you need is a guy that can troubleshoot electrical problems.. or patience and DIY time..
Sure a porsche shop may have one of those, so do lots of smaller shops.
if the guy can't check things like voltage voltage drops, continuity and resistance, he isn't worth hiring. there are licenced mechanics out there that never learned how to troubleshoot electrical circuits properly.. try not to become overwhelmed.. it's just a few circuits and each isn't very complicated on its own.. the electronics , the ECU that is a bit different.
it sounds like you may have more than one unrelated electrical issue..