starting/electrical issues

[Jezza_hr]

The starter solenoid contacts are fine, I replaced the copper connections during my rebuild and they haven't been in there long.

Voltage drop sounds like the most likely culprit when considering the starting issue coupled with the tachometer drop as Ivan has explained.

I never considered 4 gauge to be an issue as I've witnessed many people who have used it for a battery relocation before and said they haven't had an issue. I have tried a few things to compensate for the voltage drop, including a 4 gauge wire to the junction box from the alternator to make sure there's more voltage making it's way back to the battery.

As Jondee has said, using 0 gauge wire may combat the issue, but if I can rule out every other option before spending out on more expensive cable then that would be a good start. I may draw up a diagram this evening to show how things are setup.