Lookin' good, but battery cables should be at least 2 gauge when that long. You don't need that long of neg. cable, just run to frame then another short one from frame to engine block. Also run a ground strap from engine to firewall, and you shouldn't have any electrical problems. I always use 2 gauge cables no mater what the length, don't want any voltage drop due to too small of cable, the 620 electrical system is over taxed as it is, I have a 280ZX alternator on mine, and all LED bulbs, except the headlights, which are HID, and that helps, but eventually I want to replace the whole wiring harness with a better quality universal one from someone like Painless, or American auto wire. All my stock 620s when running at night with lights and heater on, when you turn on the wipers, you could hear the heater motor slow down due to not enough power, so the stock system isn't the best.
Keep up the good work! :cool: