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93 Park Ave Ultra any route for 2/0 welding cable through firewall

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Hey guys! Newbie here!


This 1993 Buick Park Avenue Ultra already had serious grounding/electrical issues that had to be rectified before a system upgrade could be considered. Purchased a 34/78 Northstar AGM deep cycle battery, 2/0 welders cable, tinned copper terminals, heat shrink tubing, 16ton hydraulic crimper, 220A DB Electric alternator and just completed the Big 4 with substantial improvements. Battery voltage at 12.8V and holds at 14.8V with full electrical load at highway speed.



Need to run 2/0 cable preferably through firewall and passenger door trim to trunk. There are body rust issues along the fuel lines where one would tie clip a power wire beneath the vehicle that have to be addressed in the future so it would be foolish to run wire outside at this time.


Hoping to run two 2/0 power lines. The first to power a 1000W inverter mounted on the floor hump between driver and passenger seats. The second run to the trunk to power two deep cycle batteries which will be installed in the spare tire pit.


Opened the dash and removed the glove box hoping to get access to what seemed to be grommets on the upper firewall.



The battery as shown above is situated on the passenger side and there are grommets (well better call them electrical junctions) on the firewall side. The space beneath these grommets is difficult to reach due to the a/c accumulator and related piping but seems the only choice. Can't find any other "grommet" type connection on the passenger side.



Any advise would be much appreciated.


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Looks super tight under the hood from those pics. Sometimes you just have to drill. I like to go in low by the floor where passenger's feet would set.

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Ace has grommet fittings, just grab some of those and drill new holes.

Sold to


Bought from




"If I was so worried about resistance I'd be unplugging the factory wiring harness, and checking resistance on every wire in my vehicle."

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At this point, I've pretty much removed as much of the dash as courage and YouTube video directions will allow. Well at least when it's time to install new radio or gauges I'll know how, but it is of no joy on this endeavor.


From the furthest depth that I can reach from the dash to the surface of the firewall is still 7 inches of Great Unknown. I probed with a tiny drill bit above the pictured wire harnesses but hit a new metallic obstruction once through the firewall and quit before I damaged something unseen so putting the dash back together now.


Ordered a step drill kit from Amazon (Home Depot wanted $74, no thanks) and the self-sealing Stinger Firewall Bushing grommet which I understand is way overpriced so will check if ACE has similar.

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