Oh, yeah, they're spendy! I use 1 gage, which is more than adequate for our purposes, and you'll get a "quick-disconnect" out of the deal from using marine-style battery clamps (if you can get them locally, great! If you can't, or don't have the time, orjust can't be arsed, I carry brass marine-style battery clamps for $5 per pair - see my website for pix and details.)
I also use welding cable, rather than battery cable (which it looks like in the pic,) which features finer strands - increasing ampacity and flexibility - and heavy-duty chemical- and heat-resistant neoprene insulation.
I also pack the crimped terminals with corrosion inhibitor, and use cold-shring tape and heat-shrink tubing to seal the ends. I've had one sitting in a bucket of salt water for the last year, and I've yet to see any signs of intrusion/corrosion when I check cable resistance.
A couple points should be noted -
J & C does two or three cables for that price - they don't do replacement alternator leads.
Replacing the alternator lead will result in removal of an OEM circuit protection device - so you do so at your own risk. Where I have measurements, I offer two kits - with and without the alternator output lead. I am working on a kit solution using an ANL fuze (the large wafer style,) and I will offer it when I've got useful measurements.
My kits also provide a replacement ground strap, from the cylinder head to the firewall - which is important for RENIX (pre-1991) applications, since the ground strap going silly will cause no end of trouble, which can be difficult to locate if you don't take a larger view of the problem.
Questions may be directed to me via PM, or to JeepI6Power AT yahoo DOT com, and many are already answered on the website. I'm working on the next round of updates to the tech archives, and I'll be answering more questions on the site as well (since I do keep track of what I'm asked, so I can make things easier to find out for everyone...)
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Edit - oops, I just took another look. They do use welding cable! My fault, I missed it... My apologies.
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