Dear friend
Yes it is necessary to change the wire gauge. Apart from having a higher current with a higher capacity alternator (55A vs. 35A) that particular cable from alternator to starter, which later from there leads to the battery, is always in bad shape. That T30 cable is originally 4mm2 square section which allows it to hold up to 28A of current without overheating in excess. See attached table. So, at least change that particular cable and if no new charges apart from original ones are added to your main fuse box, you may leave the cable T30 from starter to main light switch as is. My personal advise is to change both. Later segment may be left with a new cable with same cross area, but definitely the segment from alternator to starter should be changed for a cable with a higher cross area like 10mm2 which equals to a 8 AWG cable. Buy only cables for automotive or marine use with COPPER strands which are highly flexible and withstand 105 degrees Celsius. There are Chinese aluminium alloy cables with are cheaper but their capacity does not fulfill AWG standards.
Regards
Lp
