Just an idea for you:
Visit a boat salvage yard and take a look at some of the various boats that are being dismantled.
Find a good main harness that may be a bit longer than what yours requires.
These older harness will not offer tinned wiring. This may or may not be an issue for you. Many are still OK today after years of service. Your call on that!
Most of the older marine wiring color codes were very similar, if not the same.
If you now have helm amp meters, replace them with volt meters. (requires no additional large Amp Meter circuit(s) to the helm and back)
Helm power is typically #10 or #8 red.
Main helm Negative is typically #10 or #8 black (Negative is now yellow for today's boats).
All smaller negatives are typically black (yellow for today's boats).
Ignition.... purple.
Instrument power.... purple.
Starter motor solenoid.... yellow w/ red stripe.
Tachometer..... white or very light gray.
Oil pressure..... blue.
Temp sender...... brown or light brown.
Alternator charge lead....... #8 red... sometimes orange.
Alternator chassis negative....... #8 black on the older boats.
Alternator field....... may be it's own circuit... or it may share ignition circuit w/ a diode in the loop.
Bilge blower motor..... typically green
Bilge pump...... typically dark brown
Bilge pump float swich.... also dark brown
Cabin light negatives may be white
If you do an accessory panel, I'd run fresh dedicated Pos/Neg circuits forward for this, and not piggy-back from the helm harness.
Wire ring terminals and screw down terminal blocks can be used in lieu of the OEM harness connectors if need be.
NOTE: DO NOT use a helm Auto/Off/Manual main engine bay bilge pump switch if you plan to moor this boat.
There should be NO means of interrupting Float Switch power.
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