Alternator Wire Routing

[MaxGlide]

1977 Mercruiser 140, 42amp alternator
Replacing a blown alternator and want to make sure it wasn’t because I wired it wrong putting motor back together.
Main question I have is from alternator to switch to starter.
Do I run the charging wire from the alternator to the “both” post on the switch, then run a wire from “both” post to the starter?
ORRR…
Do I run the wire from the alternator to the starter, then another wire from starter to the “both” post? (That’s how it was.)
Essentially pic one or two?
Also, what gauge wire should I be running from the batteries at the back, to the DC panel up front, about 16 feet?

 

[dubs283]

Second picture is correct.

From alt output to main + on starter. Battery cable from starter to "common" on battery switch. Battery switch should have continuity from common to either post (1 or 2) when the switch is in 1, 2 or all, but not when off

As far as cable to the dash for accessories 10 awg or 8 awg should be okay as long as you don't have a major draw connected to it, i.e. a stereo amplifier, windlass, etc. Some boat manufacturers wire dash accessories independent of the switch, some use directly or wire through a buss/breaker panel in the bilge. Depends on boat size and number if house accessories that need DC power

 

[MaxGlide]

Second picture is correct.

From alt output to main + on starter. Battery cable from starter to "common" on battery switch. Battery switch should have continuity from common to either post (1 or 2) when the switch is in 1, 2 or all, but not when off

As far as cable to the dash for accessories 10 awg or 8 awg should be okay as long as you don't have a major draw connected to it, i.e. a stereo amplifier, windlass, etc. Some boat manufacturers wire dash accessories independent of the switch, some use directly or wire through a buss/breaker panel in the bilge. Depends on boat size and number if house accessories that need DC power

Awesome, thanks. I only have regular things like gauges and a 5” fish finder. The fish finder is wired directly to a battery as it was kicking out when we started the engine. So my plan is to use battery with the finder to start and run boat to fishing spot. Then when using battery to start and stop motor when we reposition while jigging.
Orrrr
Would it be better to run the + lead from the finder to the “both” (or common) and only start engine from 1 or 2 position?
(Never mind last part. If my goal is to avoid power fluctuations, connecting to common makes no sense. Power will always be drawn thru there.. duh)