Now that you have picked your fuse block, it is time to decide how the wires will pass through the firewall; Grommet, Bulkhead, or Pickup.
Bulkhead – The bulkhead option utilizes the GM Bulkhead firewall pass-through used in most GM vehicles from 1968 and up. The GM A-Bodies, F-Bodies, X-Bodies, etc. all used this bulkhead. Those with other vehicles wanting to utilize the bulkhead can trim their firewall to fit the GM bulkhead using the provided to-scale template in the manual.
Grommet - The grommet application allows you to route your under hood and headlight section wiring through a provided grommet, allowing freedom to pass through the firewall where you choose. Those running a completely smoothed firewall will likely prefer the grommet Pro-Series.
Pickup – The pickup option utilizes the same GM Bulkhead as the regular bulkhead application, but the tail section wires pass through the bulkhead, allowing them to be routed along the frame like factory setups. The bulkhead fits ‘68+ GM trucks, and can be trimmed to fit the ’67 or other brands and applications using the provided to-scale template in the manual.