Alternator wire going to the battery.

OK here is the thing......THERE IS ONLY ONE "switched power" wire in the engine bay from the ignition switch, and that is IT. Bear in mind there are several "things" here..........

1....that wire IS NOT FUSED originally
2....that wire may already be overloaded from age and other deterioration to the switch/ connectors/ bulkhead connector/ old wire terminals etc and suffer voltage drop.

One way "around" the situation is to electrically ferret out the "run" wire coming out of the bulkhead and cut it. Run the bulkhead connector end you cut to trigger a bosch relay, and take power fused or breaker added from the "big stud" on the starter relay, and then reconnect the engine bay end of the cut wire to the switched contact of the relay

This not only will increase the power capacity of that circuit, but will help eliminate voltage drop problems which if present, will cause OVER CHARGING of the voltage regulator

Also depending on how much power the fuel pump draws, it should have a relay as well

Your MSD "small red" is in fact a "trigger" wire similar to a relay and doesn't draw much current. That is why MSD calls for the "big red" and "big black" to have a good solid voltage source---direct to the battery/ starter relay stud