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Mounting a Fuse Block to the Firewall- 1967 Chevelle

8/24/2020
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Every old car that I’ve dragged home in the last 25 years has been a wiring nightmare. Add-on glass fuses, unfused circuits, bad splices, un-relayed accessories, I’ve seen it all. When it came time to start figuring out the add-on accessories on this Chevelle, I looked at a few different routes. One of those was to leave the factory harness in place because it was in very good condition and retained the original bulkhead connection at the firewall. This, of course, would still require the addition of new 12V constant and accessory power circuits. For which, I’d entertained adding our six circuit expansion panels. This would’ve been easy enough to pull off, considering the new underdash shelf to locate them

Just a little off the top.

However, that solution still didn’t contend with all the other changes that my car had undergone. To mention a few; One wire, 140 amp, internally regulated alternator, electric fan and fuel pump, air conditioning, simplified dash lighting and instrumentation wiring. When you compounded all the changes and re-routing that the original wiring would need to undergo in order to remain viable, it became clear.

Removing all the wiring from one of these cars is relatively straightforward, especially if the interior is disassembled. Same for the factory fuse block. With both the engine bay and lighting harnesses unplugged, the fuse block simply unscrews with two fasteners. The dash harness comes along with it.

Something old, something new.

The one thing that I really didn’t like about ditching the OE panel, was giving up the clean plug-in bulkhead at the firewall. However, I discovered a way to retain that location for routing wires and keeping a weather-tight seal. This allowed me to keep a semi-factory appearance while eliminating the corrosion hazard that the original connections had. I used a Seals-it Aluminum and Rubber Molded Grommet to create two portals. I did have to open up the original hole both at the top and bottom to create clearance for the wires. Pictured below is the first test fit. After cutting the general shape with a body saw, I cleaned and re-contoured the shape with a drum on my die-grinder.

On the engine side of the firewall, I found that one of the mounting bosses for the new fuse block aligned perfectly with an existing hole/bolt that had held the factory e-brake bracket. This placed the upper mounting hole at the top-center of the new sealing plate.

For the mounting of the fuse block itself, I used socket head (allen) bolts 1/4” x 3.5” long. For all bolts passing through the firewall and the Seals-it flange, a bead of black RTV sealant was used to ensure a weather-tight seal.

Initial test-fit of fuse block to ensure clearance and accessibility.

I found through the process of trying to route and secure wires in original channels, that self-stick insulation makes a great tool. I cut strips of Boom Matt to hold the wires where I wanted them.

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