Here's a little guide on how to chase down the current state of the wiring on your Whitby. There's a lot going on. It can be daunting. However, if you're organized, you can break it into sections, and come up with a pretty complete view of your boat's power supplies and consumption. 

Some background is in order. Our boats as commissioned so many years ago lacked modern electronics. Indeed, they lacked a solid provisioning for modern electronics. It appears that helm electronics consisted of a light behind the compass so you could steer at night. On Red Ranger, that light is part of the running lights, so we have a tiny issue sailing at night -- we have to include the "under power" lights.

When adding wind instruments, chart plotters, radars, and the like, these are profound changes. Unless someone goes to a lot of extra effort, none of these circuits will be labeled very clearly.

Also, note, the original charging systems were -- at best -- primitive by modern standards. It appears that big 1-2-BOTH-OFF switches were the standard. You selected your starting battery and started the engine. You selected BOTH to charge both banks. When the batteries were charged (how were you supposed to know this?) you switched to House. Manually. It appears this was a part of motor sailing. Later, these switches may have been supplemented by diodes so you could simply leave them in BOTH mode most of the time. 

Start with the diagrams here: https://www.whitbybrewersailboats.com/photo-gallery/whitby-42-drawings?fbclid=IwAR1kh9I0v6yfS1oY3YQh_FB3a8EJv_jthDeYuBpAgXioWM07tkb9qlUZAXM There are 8 pages of wiring diagrams that are a handy starting point. Your boat may be similar. 

Get Organized

Yes, get your pencil and clipboard, lights, overalls, and a camera. But, also break the job down into layers.

First. There's a hull grounding layer. All of the metal through-hull components are wired together. They're connected to a "dynaplate" on the starboard side. They're connected to the engine mounts, also. Generally, these are interconnected with stiff, heavy, uninsulated copper wire. The chainplates are often connected to this. It's important to chase this down, but it's also pretty easy because the wires are big and are connected to big things.

Second. There's radio antenna grounding. If you have one VHF, this is simply connected through electrical ground. If you have a SW radio, there may be a separate antenna ground plane for this. Once you locate it, you can set it aside mentally. Check it off the list of things to find.

Third. There's an AC power distribution, usually American 110V. Details vary with the owner's demands. The simplest setup was a single 30A line to a charger in the engine room and the outlets port and starboard. Red Ranger had an A/C water heater, and A/C fridge compressor, plus outlets, plus a charger. A fairly complex set of AC wires. These wires are almost always fairly large, and almost always paired in a single sheath. There will be no in-line fuses.

Fourth. Instruments data wires. An analog masthead instrument, for example, needs a bundle of wires. Wind direction, Wind speed will have separate wires, and possible a ground wire. A digital masthead instrument has a single NMEA 2000 or OneNet or Raynet cable running up to it. Analog devices connect more-or-less directly to their display units -- there will be no fuses in the wiring. Much of the engine wiring falls into this category, also.

Fifth. DC power distribution. This is the thing you were looking for. It's the bulk of the boat's wiring. It includes all DC devices, as well as solar panels and various kinds of chargers. What's important is to mentally disentangle the other wires from the DC power wiring. The DC wires tend to be small, often color-coded blue and white for the original Canadian build. New ABYC standards suggest different coloring, so it can be a rainbow of joyful wire colors.

The DC system has a further breakdown into a charging side and a load side. There may be more than one way to charge the batteries. And of course, you have a million things that want charge from the batteries

It helps to remain organized and chase down the wiring in pieces. Otherwise, this process can be daunting.

The AC Side

AC wires are big, often paired, and relatively easy to track. 

If you have shore power, unplug before examining the AC side.

If you have an inverter, turn it off. All the way off. If your inverter has a automatic switchover relay so it goes on when shore power goes off, consider turning off your house batteries to make sure it's stone dead and will not spring to life.

Once the AC power is off, you can open the electrical panel and take off any protective cover on the AC side. Red Ranger has a big aluminum plate to keep fingers and tools away from the AC connections.

You should be able to start at the boat's connector(s), which is (are) just aft of the power panel. You should be able to follow the wires to the circuit breakers. There's generally a big old "bus bar" for the neutral part of AC circuit, and individual breakers for the "hot" part. Often it's black wires for hot and white wires for neutral.

Each breaker will connect to a pair of wires that goes forward behind the bookshelf, down behind the cabinet in front of the fuel tank, and under the passthrough to the engine room. For the most part, the destination should be pretty clear and match the label on your panel.

One pair of AC will go about two feet aft to an outlet right near the panel. This is connected to the three other outlets on the starboard side. 

There are two common sources of mystery.

1. The unlabeled breaker. This often involves trying to follow the wire down under the passthrough where it vanishes under the cabin sole. Does it go forward? Aft? Engine room? You'd like to be able to wiggle it at the panel and see what wiggles elsewhere on the boat. That should be hard to do. The wires should be locked down with cable ties every few inches. We'll return to this.
2. The disconnected wire. This happens when something was removed and the wire left in place. This can lead to cutting and replacing a lot of cable ties. In some cases, you can pull the wire through. In some cases, you'll cut the wire into sections and pull each section out.

You can -- with some care -- follow AC wiring around using a volt-ohm meter. First. Be sure the AC side is stone dead. Disconnected from shore power dead. Inverter turned off dead. (If necessary, house batteries off, or, if you're still unsure, disconnected from the batteries dead.)

For each AC thing (fridge, water heater, charger, air conditioner, etc., etc.) do the following steps:

1. Short-circuit the wires at the thing. A pair of alligator clips and a short span of wire will do nicely to short it out. For an outlet, you can often jam a wire across the plug connectors.
2. Walk (don't run) back to the panel.
3. Put your volt-ohm meter continuity tester on the unlabeled breaker and the ground bar.
4. Listen for the continuity test beeper. If there's continuity from breaker out to thing, across your jumper, and back to the neutral bus, the alligator clips shorted out the circuit. This means you found the thing. Update your drawing. Label the circuit breaker. Remove the alligator clip. 

If there's no continuity, you didn't find a connection from your panel to the thing and back to your panel. It helps to then check all the other breakers to be sure things are working as you expect. Eventually you should find one of the circuit breakers is properly shorted. It's difficult to correlate breakers from the back of the panel to the front. You'll want to label them on both sides.

This trick saves you from having to have your hands on both ends of the wire. Instead of having one probe at the panel and one probe somewhere else on the boat, you make a loop somewhere else on the boat, and hunker over the panel trying to find both ends of the loop.

The DC Side

The DC system is a bit more complex. We'll start from the ground (negative) side, because that's often simpler.

The DC system ground includes a number of things.

• The negative side of all your batteries.
• The engine.
• There will often be DC Ground bus bars. The forward wall of the engine room, up high, often has a strip with a milion ground wires returning to it. On Red Ranger, this is connected to a second grounding bus bar down near the forward, starboard motor mount.
• Ground bus bars will connect to the motor mount. On Red Ranger, the motor mount stud has the bus bar wire, the alternator ground, and the immense battery ground.
• The battery ground wire is big and passes through a "shunt" before connecting to the batteries.

The shunt (https://www.electricalhub.com/blue-sea-8255-8255-dc-digital-meter-shunts) is a big brick of metal with a known resistance (something like 1 ohm) that's used to measure current flowing through your system. Two small wires connect the shunt to the amperage display on the electrical panel. 

The older panel meters (with needles) often used a shunt on the positive side of the circuit. This shunt will be on the back of your electrical panel. It's the same basic idea: a known resistor used to gauge current flow.

In the end, DC grounding is a bunch of interconnected bus bars, most of them in the engine room. One very long bus bar would be fun, but impractical, so a number of shorter bus bars is more common.

Engine Wiring -- Charging, Load, and Meters

There are three parts to the engine's wiring. It is a charging system (via the alternator) as well as a load (via the starting solenoid), and it has data for the engine instruments.

Engine Charging is -- traditionally -- the only charging. The alternator has loops of wire and electro-magnets. A wire passing through a magnetic field is the definition of electricity. A set of diodes converts the constantly alternating current into direct current that charges the batteries.

The original alternators produced a maximum of 55 or so amps. And that was at top RPMs; at 1250, it could barely produce 20A. A replacement Balmar alternator can produce 110 amps at top RPMs. This requires something like 6 gauge wire. It's pretty big.

In addition to engine charging output, the starter motor is a load. There's a positive feed to the solenoid. It starts at the panel, runs up to the key and starter button on the pedestal, then back down to the solenoid on the starter. When you turn the key and push the button, power flows to the solenoid. It trips the solenoid inside the starter that's connected directly to the starting battery and ground by immense 0 gauge wires. (You can short the connections on the starter, also. Be sure you're clear of the belts when you try this.) 

The other wires from the engine are sensors that go up to the pedestal to report oil pressure, engine temperature, alternator pulses (converted to RPM's), and (maybe) voltage levels.

The starter battery should go through some kind of switch. An old 1-2-both-off switch may be in place. Red Ranger has a newer BEP system with switches and a voltage sensitive relay. You should be able to turn off the batteries so you can disconnect them and replace them safely. These are BIG wires. 

Looking at the starter battery. It has a big, 0-gauge wire to the switch. A big, 0-gauge wire back to the starter. It has a big 0-gauge return to the shunt, and from there to the battery. 

Red Ranger was originally wired with an ammeter in the binnacle. That meant a wire from the alternator up to the binnacle first, then back down through the engine room, and up to a circuit breaker on the electrical panel. From there it went and from there to the positive side of the panel where it could charge the batteries. That's a lot of distance. I've removed the ammeter so the power goes from alternator to a fuse to the positive side of the battery bank. I have a separate ammeter on the panel. I put a simpler voltmeter on the binnacle.

Batteries require fairly high voltage to charge. Red Ranger has wet cell batteries and they charge at 14V. So the voltage level tells me if we're charging, or if we're done charging because the batteries are full.

House Load

The largest part of the system is the house load wiring. A lot of Whitby have a power distribution block in the engine room. Originally, this had a neatly typed label with all of the wire destinations. The idea was for the panel wires to connect to this block, and the wire to the thing would leave this block. They were all labeled so you could more easily diagnose problems.

It's unlikely any of the new systems were added to this wire block.

And it's really unlikely anyone updated the label on the wall next to the block to explain what the wires did.

However, it is a good starting point. You can list the things on the label card as a preliminary wiring diagram.

You can then confirm them with your volt-ohm meter. For this, you'll need to have power on in general, but almost all the circuit breakers off. All but the thing you're testing. 

Let's say you want to find wires for the port-side light in the V-berth. 

 Follow these steps:

1. Turn the thing on. 
2. Turn on the right circuit breaker. For example, Red Ranger has a circuit breaker for port-side interior lights. Turn this on. The light goes on. 
3. Put the positive side of your meter's voltage probe on the wire in the block in the engine room labeled something like "Port Lighting".
4. Put the negative side on the nearby ground bar.
5. The meter should read ambient system voltage (over 12.5V unless your batteries are on their last legs.) This means you found the thing. Update your drawing. 

If the thing you turned on is not connected through the wire on the distribution block in the engine room, you'll see the thing working, but you won't see voltage on the expected wire in the block.

Two things can be wrong when the thing is working, but we can't see voltage in the distribution block:

• The labels aren't right. 
• It doesn't go through the distribution block in the engine room.

If you probe all the wires on the distribution block and one of them shows voltage, that's the working wire. Update the label.

If none of those wires have current. Then. Well. The wire follows a different route. This can be challenging to track down.

For now, however, you know it works. You can update your diagram.

Focus Is Important

The essential ingredient here is focus. There are a lot of wires, but they have different purposes. If we distinguish the general wiring area, we can decompose a large and complex problem into a number of smaller, and simpler problems.

All of the electrical concepts can be summarized as a "circuit". Electricity (conceptually) starts at the positive side of the battery. It runs to the circuit breaker panel. From there, it is split out into smaller, focused loads. Most loads go to a connection block in the engine room (a few go directly to the device.)
Most devices will have a fuse near the device. There's a return that goes to one of the ground bus-bars. The ground bars, eventually, connect back to the negative side of the batteries.

It's relatively safe to put your Volt-ohm meter test probes on live DC connections. If you have a good ground connection, you should see familiar-looking voltage readings to show the wires full to the top with electricity.

Other Charging Systems

Charging systems are the opposite of a load. They operate at higher voltage, and (in effect) push current into the batteries by pushing against the normal flow out of the batteries. Most boats will have three separate charging systems:

• The Engine Alternator.
• Shore Power Charger.
• Solar Panels (or wind or a towed generator.)

The engine alternator is a pretty slick device. Above, we noted that it's coils of wire and electro-magnets. When a wire moves through a magnetic field, that's electricity. The altenator's electro-magnets work by bleeding a little of the alternator's output current back into the alternator. A very simple alternator will use a fixed "regulator" attached to the housing to do this.

A fancy Balmar alternator will have a separate, external controller. The controller will be monitoring the output voltage from the alternator. When the engine starts, and the alternator starts spinning, the controller will put only a tiny bit of current into the electro-magnets. Enough to count the rotations, but nothing more. After about a minute (when the engine is clearly running) the controller will ramp up current to the electro-magnets. This puts a load on the engine and starts charging the batteries.

The shore power charger is (potentially) very simple. It lives in both AC and DC worlds. It could be a transformer and a handful of diodes. The components cut the 100V AC down to 14V DC to charges the batteries. This is primitive (but workable) until it boils the chemicals in the batteries. 

Modern shore power charges have complex charging cycles with a bulk stage, an absorption stage, and a float stage. They live in the same place in your wiring diagram. They're on the AC side, producing current for the DC side. 

Shore power chargers are often protected by a large fuse. The Mastervolt charger on Red Ranger can produce something like 70 amps. It has a huge fuse and a huge wire to the batteries.

A solar system is *also* connected into the positive side of the power system, in parallel with shore power and the alternator. We have a 30A solar controller. We have a solar panel bus bar that has a number of solar panel wires entering it. (We have seven panels on deck in various places.)

All of the charging systems are in parallel with each other. They're connected into the system via the BEP 716 voltage sensitive relay. When the voltage in the starting batter gets above 13.7V, the batteries are bridged and they can both charge.

Here's the Red Ranger charging diagram.

This shows the Mastervolt shore power charger, the Alternator, and the "Other Source" (code for Solar Panels) all connected to the "A" connector on the BEP switch. This is also the positive side of the engine battery. 

The "C" connector of the BEP switch is automatically connected if the VSR sees 13.7 volts.  It can also be manually connected with the emergency parallel switch.

The "D" connector is the "House On" part of the BEP switch. We summarize most of the boat with a single box. Another diagram has details.

The "B" connector is the "Engine On" part of the switch. We show a solenoid icon here. There's a second connection to the starter motor from the engine battery. It's not shown here because it's more part of the engine than it is the DC charging systems.

The little "(A)" in a circle is the Blue Sea ammeter, connected on the negative side of the system.

The little *(V)" in a circle is the Blue Sea voltmeter, connected into the positive side of the system. There's a switch there to allow the voltmeter to check house or engine. 

The "Bilge Pump #2" is a bilge pump wired directly to the batteries with only a fuse. It cannot be turned off.

Your boat may be different. What's important is decomposing the various electrical systems into subsystems to help manage the complexity. Rather than cram everything into one picture, it helps to focus on part of the system, summarizing other parts as big boxes that can be viewed separately.