I wouldn't use butt crimps as those are ugly, bulky, and preferred by gomers. There are many approaches. I think most manufacturers dropped bulkhead connectors by the 1980's as the number of wires thru the firewall grew. I know that mid-1980's GM pickups I've picked for HEI just run the wires straight thru a grommet in the firewall. My 1996 Plymouth hard-wires straight thru to the underhood relay/fuse box. My 2002 Chrysler does similar, but has multiple connectors on the bottom of the relay/fuse box, and those give Northerners endless problems with corroded pins. My 1984 M-B is a strange in-between. They put the fuse box right in the bulkhead, though all wires connect to it on the cabin side, then some pass thru a large grommeted hole to the engine bay. I have seen some people install a many-pin Amphenol connector in the bulkhead. Those are common in aerospace and can be pricey unless one follows you home from work or better find cheap on ebay. I can't think of any other inexpensive connectors with many pins which are high-quality. Indeed, I have had to pay $$$ for industrial connectors for servo motors and such. For early-A's where only 2 connectors are needed since the wiper motor was still in the cabin, a 1965 bulkhead connector is best since it sends the high ALT and BAT wires thru on dedicated buss-bars (no melting). I retrofit one in my 1964 Valiant, only having the cut the square hole 1/8" taller to fit. 1963 also had that, but w/ fewer terminals. The "fleet wiring" in later years ran those thick wires thru grommeted holes, separate from the bulkhead connector.
