The bulkhead connector terminals are unsealed. As such, the terminals will begin to oxidate/tarnish with time. Those in damp, harsh, environments will corrode. These factors further negatively impact the current capacity of the terminal. To the point that even a stock electrical load is more than they accommodate without overheating. As the connector's current handling ability decreases, the voltage drop across it increases. This voltage drop can and does impact a number of things. Even a minor voltage drop can cause aftermarket electronic ignitions to miss, especially at idle, or completely shutdown.
Some have bypassed the bulkhead all together as a remedy. This usually eliminates the functionality of the amp meter, as a side effect. More seriously, they often eliminate the fusible link and provide no replacement overcurrent protection. This exposes their vehicle to a fire hazard in the event of an alternator rectifier failure, damaged wiring in a wreck, or other conditions that will create an overcurrent, wire melting, condition.
Some point to the amp meter itself as an issue. To the contrary, the amp meter is very robust. As an example, we had a couple of late '70s stepvans with Ford chassis. With that, Ford instrument clusters. They had an amp meter, but as with nearly all Ford and GM vehicles with amp meters in that period, they were a shunt fed meter that never seemed to work and was nothing more than a dash ornament. A functioning amp meter was very important to us as we had high electrical loads in these trucks: halogen headlights, three heater blowers, 1000 watt inverters, multiple batteries, etc. When outfitting the trucks, we removed the Ford amp meter and replaced it with an inverted amp meter from a '70 B-body Mopar. It fit directly in the same place and the graphics were very close. Of course, this required a direct feed through connection. These Fords were equipped with 90 amp alternators and the Mopar gauge never failed nor indicated any signs of overheating.
My goal was to reinforce the bulkhead connections,increase the ampacity, and retain the amp meter. This could be accomplished in a number of methods. I finally decided on re-utilizing the factory wiring, in part, and continue to utilize the bulkhead as the feedthru point.
Bulkhead Connector
The bulkhead connector's far left cavity section is unused, in at least the later year sweptlines. It has spaces for eight terminal feedthrus. I would utilize four, in parallel, for the alternator connection and the other four to be used for the battery connection. While these terminals are rated for up to 48 amps, that is well beyond my comfort level for such. I'm more comfortable with 25 amps continuous and 30 amps intermittently. As such, this would yield a bulkhead through connection ampacity of 100 amps continuous and 120 amps intermittent.
Cab Wiring
The factory alternator and battery feeds are #12 gauge wire. While this might support intermittent loads of 40+ amps, it would have significant voltage drop. So the wiring will require an ampacity increase, as well. I gave some thought to replacing the alternator and battery wiring with #8. However, #8 can be difficult to work with and splices become quite large and unevenly contoured. As such,I decided to retain the factory #12 wiring and parallel it with #10. The combined ampacity of #12 and #10, in parallel, is actually a bit greater than #8.
I began on the cab side with partially removing the instrument cluster, fuseblock and bulkhead. My bulkhead shells and terminals were in good condition. I extracted the battery and alternator feeds from the bulkhead. With the female terminals being in good condition, I re-used them, squeezing the terminal rolls gently with a pliers to tighten their connection to the mating male terminal. A few inches back from the terminal, I stripped off a 1/2" or so of the insulation, without cutting the wire. I wrapped a matching color of #12 wire around the stripped area, soldered, and taped with quality Super 88 tape. I then trimmed the other end of the add-on #12 wires to match the length of the factory wires. I crimped and soldered, both, a female terminal to the end. I inserted these in the far left cavities with black alternator wires in the top four group and the red battery wires in the bottom four group.
As it is much easier to solder on the bench, I stripped back black #10 wire and two black #12 wires, soldering the two #12s, in parallel, to the #10. Considering the mass of these, I gently clamped the #10 in a vise and utilized a propane torch to heat the wires until they melted the solder. I cooled the connection with a wet paper towel. With aluminum protective jaw covers in place on the vise, I then squeezed the solder connection, in the vise, to flatten the joint contours, while rotating a few times between squeezes. Once somewhat smoothed, I re-heated the connection, with the propane torch, to re-flow the solder. This repaired solder connections that may been cracked or fatigued by the squeezing. Once cooled, I applied 5/16 heatshrink over the splice. I trimmed the #12 wires to within a few inches of the splice. I then crimped/soldered female terminals to each #12 wire. I repeated this process utilizing red wires.
Next, I inserted the #12 tails/terminals, of the #10 wires, into empty terminal locations of the corresponding bulkhead four terminal groups. I routed the #10 wires along the factory harness, tie wrapping to it, to the instrument cluster. I terminated the #10 wires on the amp meter studs along with the color matched factory wiring. I know have a #12 and #10, in parallel, from the bulkhead to the amp meter, for the alternator and battery feeds each.
Alternator Wiring
Again, I paralleled a #10 wire from the alternator to the bulkhead connectors. As it is easier to solder on the bench, I began soldering two #12 tails to the #10 wire and crimping/soldering the male terminals to each. I unplugged the engine harness from the bulkhead and released it from the firewall retaining clips. I could then bring the bulkhead end of the harness to the top of the right inner fender, making it much easier to work upon. I disconnected the #12 factory harness wire from the bullet connector just behind the bulkhead terminal. I cut off the bullet connector and soldered two #12 black wire tails to where the bullet connector had been attached, sealing this splice with 5/16 heatshrink. Male terminals were crimped/soldered to the other end of those tails. Those male terminals were inserted into the top four position plug for the far left bulkhead cavity. The male terminals, soldered to the #10 tails, were inserted into the two remaining positions.
The fusible link cannot be modified to accept the wire tails required with the four terminal bulkhead plug. Nor is its current capacity adequate for the increase in ampacity. I replaced the fusible link with a high amp, waterproof, circuit breaker. I chose the manually re settable type for two reasons:
1. If an overcurrent condition occurred, I did not desire the circuit breaker to continuously cycle through trip/reset cycles. This would still allow the wiring or device subject to the overcurrent condition to partially heat up.
2. This type of breaker was also manually trippable. This provides an easy means to disconnect the battery, for service, without actually having to remove the battery cable from the post.
