Over the past decade or more, "regular" electrical topics come up repeatedly. In developing responses to questions, many of us use the handy links to earlier discussions. I've developed this "Electrical 101" topic, which is a group of links to popular subjects and those discussions. Many of them include links to other websites and message boards, since boat electrical systems are not boat-specific. Many thanks to Maine Sail, not only for his contributions to this message board, but for his "Musings with Maine Sail" on
www.catalinaowners.comhttps://forums.sailboatowners.com/forums/musings-with-maine-sail.135/ and his own website:
https://marinehowto.com/You could buy a few good books (see Reply #7 below), or you could read this stuff.

Good luck.
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Here are some good "intro" courses for Electrical Systems:
The All-Important Energy Budget:
http://c34.org/bbs/index.php/topic,3976.0.htmlIMPORTANT BASICS What are amps & amp hours (thanks to StuM from CF.com)
http://www.cruisersforum.com/forums/f14/amps-v-amp-hours-v-amps-hr-154363.html#post1933764Record of Daily Energy Use of 100 ah per day:
http://c34.org/bbs/index.php/topic,6353.msg41471.html#msg41471Largest House Bank 101 (by Nigel Calder)
http://c34.org/bbs/index.php/topic,5807.msg45046.html#msg45046and Maine Sail's excellent writeup:
https://forums.sailboatowners.com/index.php?threads/multiple-house-banks-vs-one-house-bank.184137/&highlight=windlassNEW March 2022 LifePO4 Batteries on Boats (Maine Sail)
https://marinehowto.com/lifepo4-batteries-on-boats/Why jump start packs make little sense (isn't turning a switch easier than wiring something together when things are dicey???)
https://forums.sailboatowners.com/index.php?threads/battery-modifications.193743/#post-1489220Reverse Polarity 101 from BlueSea:
https://www.bluesea.com/support/articles/AC_Circuits/90/Reverse_Polarity_IndicatorsWire Sizing Tables from West Marine (unfortunately they removed the handy charts! around 2016)
http://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity www.bluesea.com also has good material on this and fusing, but it's a PDF download and doesn't link. Here's the link to the page, scroll down for the PDF download of the Protect Your Boat With The Correct Size Wire And Fuse - Wire Size Chart:
https://www.bluesea.com/support/reference which links to this table:
https://d2pyqm2yd3fw2i.cloudfront.net/files/resources/reference/20010.pdfBattery Fuse Sizing from Maine Sail
https://forums.sailboatowners.com/threads/battery-fuse-sizing-how.130775/Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams
http://c34.org/bbs/index.php/topic,4949.0.htmlThe Ample Power Primer
http://www.amplepower.com/primer/primer.pdfSorry, link is gone, Ample Power unfortunately closed. They were so ahead of their time! [May 2019]
The Ample Power Primer is still available on the Wayback Machine at
https://web.archive.org/web/20160323132827/http://amplepower.com/primer/primer.pdfIt remains one of the best...
Many thanks to Bill Murdoch
OEM 1-2-B Switch Wiring History
http://c34.org/bbs/index.php/topic,4949.msg30101.html#msg301011-2-B Considerations (New 2020 - Rod finally got around to diagramming what I had done in the above link in 2009 :) )
https://marinehowto.com/1-2-both-battery-switch-considerations/Basic Battery Wiring Diagrams
This is a very good basic primer for boat system wiring: http://c34.org/bbs/index.php/topic,6604.0.html This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowners.com/showthread.php?t=137615This is a newer primer for boat system wiring design with a thorough diagram: Building a Good Foundation (October 2016)
http://forums.sailboatowners.com/index.php?threads/building-the-dc-electrical-foundation.181929/#post-1332240The Short Version of the 1-2-B Switch Stuff:
http://c34.org/bbs/index.php/topic,5977.msg38552.html#msg38552 This is a link to the Electrical Systems 101 Topic, reply #2
How to properly wire & switch a DCP switch - Maine Sail's "workaround" explained Replies #28 & 29
https://forums.sailboatowners.com/threads/what-size-fuse-for-automatic-charging-relay.1249932137/page-2Maine Sail's DCP Wiring Diagram
https://forums.sailboatowners.com/threads/operating-the-house-start-battery-selector.1249933496/#post-1745066AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
https://forums.sailboatowners.com/index.php?threads/darn-agm-batteries.133773/What are ACRs, Combiners & Echo Chargers? (by Maine Sail) [scroll to the top]
http://forums.catalina.sailboatowners.com/showthread.php?p=742417 and
http://c34.org/bbs/index.php/topic,9404.msg70131.html#msg70131Making Sense of Automatic Charging Relays (2019)
https://marinehowto.com/automatic-charging-relays/Basic Battery System Descriptions (bottom of page one, then to page two)
http://forums.catalina.sailboatowners.com/showthread.php?t=104505another good discussion, scroll to the top to start:
http://forums.catalina.sailboatowners.com/showthread.php?p=680363&highlight=duo%20chargeLoaded Battery Voltage vs. SOC - AGM Lead Acid Battery by Maine Sail --- why using battery voltage as an indicator of battery SOC is something that requires thought & understanding.
http://forums.sailboatowners.com/index.php?threads/loaded-battery-voltage-vs-soc-agm-lead-acid-battery.176854/20 Hour Capacity Test by Maine Sail
http://forums.sailboatowners.com/index.php?threads/battery-replacement-agm.179118/#post-1295253Alternator Installation 101 [new Nov. 2018 from Maine Sail]
https://marinehowto.com/marine-alternator-installation-tips-tricks/Alternator heat, Regulator Controls, Small Engine Mode
http://c34.org/bbs/index.php/topic,4454.0.htmlSmall Engine Mode - discussion with link to the picture of the toggle switch:
http://c34.org/bbs/index.php/topic,4454.msg27149.html#msg27149Small Engine Mode - the picture of the toggle switch
http://c34.org/bbs/index.php/topic,4669.0.htmlAlternator Repair Shops
https://c34.org/bbs/index.php/topic,7917.msg55085.html#msg55085Using a 3/8" Belt on a Larger Alternator
https://c34.org/bbs/index.php/topic,10702.msg83288.html#msg83288Programming a Balmar Voltage Regulator: (Thanks to Maine Sail)
https://marinehowto.com/programming-a-balmar-voltage-regulator/Ammeters & Shunts 101:
http://c34.org/bbs/index.php/topic,6032.0.htmlBreaking in New Wet Cell Batteries:
http://c34.org/bbs/index.php/topic,6353.0.htmlUnderstanding Batteries
http://c34.org/bbs/index.php/topic,6488.0.html with a link to another website
What is a Deep Cycle Battery? (from Maine Sail's website)
http://www.pbase.com/mainecruising/deep_cycle_batteryBattery Acceptance by Stu
http://c34.org/bbs/index.php/topic,4787.0.htmlWhy Going Into FLOAT is NOT Full
http://c34.org/bbs/index.php/topic,8216.0.html10-18-13 LINK BROKEN Battery Acceptance (a very good Maine Sail presentation and further discussions)
http://forums.catalina.sailboatowners.com/showthread.php?t=114054 10-18-13 LINK BROKEN Battery Acceptance Observations by Maine Sail
http://forums.catalina.sailboatowners.com/showthread.php?p=674108&highlight=battery%20acceptanceOvercharging with Combiners or ACRs The MYTH:
http://c34.org/bbs/index.php/topic,7052.0.htmlAGM Batteries - Making The Choice (from Maine Sail)
https://forums.sailboatowners.com/index.php?threads/agm-batteries-making-the-choice.124973/AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
https://forums.sailboatowners.com/index.php?threads/darn-agm-batteries.133773/Additional Observations on the Limits of AGMs
http://c34.org/bbs/index.php/topic,5977.msg63004.html#msg63004Automotive Alternators vs. Deep Cycle Battery banks (by Maine Sail) (NEW March 2016)
http://www.pbase.com/mainecruising/automotive_alternators_vs_deep_cycle_batteriesAlternator Upgrade - a 2018 thread with input from Maine Sail
http://c34.org/bbs/index.php/topic,9773.0.htmlAlternator Regulator Wiring Diagrams - all three
http://c34.org/bbs/index.php/topic,4548.0.htmlAlternator Regulators - The Differences between ARS-5 and MC-614 Units (scroll UP to see reply #5)
http://forums.catalina.sailboatowners.com/showthread.php?p=1103132How Alternators & Regulators Work PLUS External vs. Internal Regulators (by Maine Sail):
http://forums.sbo.sailboatowners.com/showthread.php?t=125392Alternators & Voltage Sensing (by Maine Sail):
http://www.pbase.com/mainecruising/regulator_voltage_sensingUniversal M-25 & M25XP Alternator Bracket Upgrade & Alignment
IMPORTANThttp://c34.org/bbs/index.php/topic,7917.0.html
and
http://c34.org/bbs/index.php/topic,9380.0.htmlGolf Cart 6V Battery Wiring
http://c34.org/bbs/index.php/topic,7162.0.htmlStu's Wiring Diagram
http://c34.org/bbs/index.php/topic,4623.msg27335.html#msg27335Power Share Feature for Link 2000 Controlling Honda Generators
Very helpful hint to control generators and 20A shorepower
http://c34.org/bbs/index.php/topic,1474.0.htmlSolar Systems: Selection, Installation & Controllers by Maine Sail
SUPERB http://www.pbase.com/mainecruising/solar_panelDo I Need a Controller for Solar?
http://forums.catalina.sailboatowners.com/showthread.php?t=144557Sizing wiring for solar
http://www.freesunpower.com/wire_calc.phpHow to Wire a Battery Monitor by Maine Sail:
http://forums.catalina.sailboatowners.com/showthread.php?t=125606New
SMART GAUGE Battery Monitor
http://www.pbase.com/mainecruising/smart_gaugeConverting a Leece Neville Alternator to External Regulation by Maine Sail
http://c34.org/bbs/index.php/topic,4879.0.htmlAlternator Sources by Maine Sail (Reply #16)
http://c34.org/bbs/index.php/topic,5686.15.htmlAlternator Source from Leo310 Total Parts Canada
https://www.totalpartscanada.com/alternators/#/filter:categories_hierarchy:Alternators$253EMarine$253EUniversal$2520Fit
Wiring a new charger From Maine Sail:
http://forums.sailboatowners.com/index.php?threads/marine-battery-chargers-installation-tips-considerations.136765/#post-880275 and
https://marinehowto.com/installing-a-marine-battery-charger/IMPORTANT Advice on these charger settings:
http://c34.org/bbs/index.php/topic,5977.msg63001.html#msg63001Echo Charger Use
Warning from Maine Sail:
http://www.sailnet.com/forums/electrical-systems/72295-xantrex-echo-charger-rant.htmlInstalling Battery Selector Switches (the "posts" in the back
don't physically match with the switch positions on the front)
http://c34.org/bbs/index.php/topic,6911.0.htmlremoved dates added 7/30/12 
Engine Starting Loads - Amp Draw Data (by Maine Sail)
LINK 404 don't use
http://forums.catalina.sailboatowners.com/showthread.php?t=102027Battery Fuse Sizing - from Maine Sail
https://forums.sailboatowners.com/threads/battery-fuse-sizing-how.130775/WalMart Battery Source
http://forums.catalina.sailboatowners.com/showthread.php?t=136852Battery Equalization 101
http://forums.catalina.sailboatowners.com/showthread.php?t=148505SMART PLUG by Maine Sail
http://forums.catalina.sailboatowners.com/showthread.php?t=159096&highlight=smart+plugSMART PLUG Installation Tips by Rick Allen
http://c34.org/bbs/index.php/topic,8460.0.htmlDifferences between Balmar MC-614 and ARS-5 Regulators 101
http://forums.catalina.sailboatowners.com/showthread.php?t=160744&#post1102540http://forums.catalina.sailboatowners.com/showthread.php?p=1053410&highlight=ars-5Programming a Balmar External Voltage Regulator
https://marinehowto.com/programming-a-balmar-voltage-regulator/Blue Sea Tables
https://www.bluesea.com/support/reference Scroll down to find the PDF download: Protect Your Boat with the Correct Size Wire & Fuse Chart. Handy to keep around.
Wire Size Calculators 101
http://www.genuinedealz.com/voltage-drop-calculatorhttp://www.bulkwire.com/wireresistance.aspAir Conditioning Electrical 101 by Maine Sail
http://c34.org/bbs/index.php/topic,8710.msg61930.html#msg61930Seaward Panel History (thanks to Paul Alcock)
http://www.whalepumps.com/marine/siteFiles/resources/docs/Seaward/manuals/ElectricalPanels.pdfBypass The Orange/Red Circuit - Maine Sail's version of the wiring harness crap, but includes a good discussion of the wires at the back of the old OEM alternators
http://www.pbase.com/mainecruising/universal_wiring_harness_upgradeRaymarine Repairs
http://c34.org/bbs/index.php/topic,7129.msg56425.html#msg56425Grounding a Honda Generator
http://c34.org/bbs/index.php/topic,6122.msg39290.html#msg39290Beneteau Wiring Diagrams - Maine Sail's corrections - Just in case you have a friend with a Beneteau and want to help him with his unusual switching Reply #8
https://forums.sailboatowners.com/index.php?threads/one-black-and-two-red-electrical-switches.191463/#post-1456512