In a fiberglass trailer forget all you know about 12 volt automotive wiring, think residential wiring,
all circuits need two wires, fiberglass does not carry current.

12 Volt Coach Wiring

White wires are ground wires ( - ), black wires are power ( + ), this can cause confusion when connecting to a battery, the negative post is usually black and the positive red so you will be hooking a white wire to a black post.

Deep Cycle batteries have threaded studs with wing nuts connected to the posts, the negative stud is usually smaller than the positive one, the terminals on the leads should be two different sizes as well so that they can only be connected one way.

Always use a Deep Cycle battery, they are made to be constantly drained and recharged so will last much longer than a typical automotive style battery. Try to recharge them when they are depleted to 50% of their capacity.

Deep Cycle batteries come in different types, 24, 27 and 29, the larger the number the larger the physical size and more amp/hrs available. A 27 will give about 50% more amp/hrs. than a 24, a 29 will double a 24.


Getting a good ground is key to solving most 12 volt problems in a Boler or any other fiberglass trailer.

Two methods can be used for this, grounding the battery to the frame and connecting to it in the vicinity of the light or running a wire directly from the battery to a common binding post in a central location and connecting the lights to it.

Other Sources Of 12 Volt Power

In addition to batteries, 12 volt power may be obtained from solar panels, generators and converted from 110 volt outlets. For solar panels to be effective they have to be very large and so are not generally practical for use with a Boler, though some people do use them. Generators, with a couple exceptions, are noisy and don't usually endear you to other campers. Most converters are equipped with a charger to keep the battery fresh.

110 Volt Wiring

110 volt power may be obtained from an outlet at a camp site or from a battery using an inverter. Inverters are available in different sizes from small models supplying 50 watts that plug into a cigarette lighter outlet to larger units hard wired into the system supplying 100's of watts. Unfortunately no matter how large the inverter the output is limited to the storage capacity of the batteries on board so they are more suitable to run appliances with a low current draw such as radios or laptop computers than high demand appliances such as hair dryers and toaster ovens.

Towing Wiring

A word of caution before wiring your vehicle for towing, unless you know exactly what you are doing go with the 4-way flat style plug. Using the Six or Seven style connectors allow you to connect the coach or the coach battery to your tow vehicle's electrical system. Today's vehicles have very complicated and expensive electrical systems, just one "oops" can cost hundreds of dollars.

If you wish to connect your vehicles alternator to your coach battery an isolator should also be installed so that your vehicle battery will not become discharged when you are parked.

4-way flat

The common configuration on a Boler is a 4-way flat plug. This system runs the running lights, it does not charge your battery or supply power to the coach, there are only four wires involved.

White - Ground, this is the exposed prong on your vehicle.

Brown - Running/Marker lights, includes licence plate light, tail lights and the side amber and red clearance lights.

Yellow - Left turn/Brake

Green - Right turn/Brake

Download .pdf diagram

Six-connector plug

If you have electric brakes you may have a six-connector plug, it also includes a 12 volt power wire.

Black - 12 volt power.

White - Ground.

Brown - Running lights.

Yellow - Left turn.

Green - Right turn.

Blue - Electric brakes (if equiped).

Seven-way plug

This is a newer style plug that is now pretty well standard on RV's.

#1 White - Ground.

#2 Blue - Electric brake.

#3 Green - Tail/Running lights.

#4 Black - Battery charge.

#5 Red - Left turn/stop.

#6 Brown - Right turn/Stop.

#7 Yellow - Auxiliary/back-up.

Download .pdf diagram


This is a general guide, always test before connecting your wiring.

If you are trying to wire a car/truck that has separate turn and brake lights to a trailer where they are one piece you are going to need a converter.

Emergency Flasher for 7 Way Plug

A simple device, that can be constructed at very low cost by just about anyone, assures that your rig will be brightly lit in the event you have to leave your trailer on the side of the road, it will flash your trailers clearance lights and will be seen for miles.

You can build this yourself or have your local R.V. supply store make one for you.

Parts required:

One seven pole socket (same as on your tow vehicle)
One flasher unit
Two pieces insulated automotive wire (14 gauge, 10" long)
Two crimp on wire connectors (to fit terminals of flasher unit)

Assembly instructions:

Remove the two phillips head screws on the side of the 7 pole socket, allowing you to remove the terminal block from under the spring loaded cover.
Insert two of the wires through the back of the socket so that they protrude through the cover and strip off 1/4" of the insulation.
Attach one wire to the terminal marked "Black" and the other to the terminal marked "Green".
Reinsert the terminal block in the socket housing and reinstall the screws. Also tighten the clamp at the rear of the socket at this time to hold the wires in place. You might have to wrap the wires with tape so that the clamp will tighten up on them.
Next, bare 1/4" of the other end of the wires and crimp on the blade type connectors.
Now simply plug these connectors onto the two prongs of the flasher unit and tape everything up securely.
Presto, you're done. Try it out on your trailer to make sure you've done everything correctly. Your rig must have a coach battery installed for this to work.
When you plug your trailer cord into the socket, the power from your battery (the "Black" terminal) is sent through the flasher and on through the "Green" terminal to the running lights on your rig, making them flash on and off. Now you can safely leave your rig at night to make an emergency run with the tow vehicle.

LED Light Conversion

Of all the modifications I have done this is probably the most significant, if you have ever followed a Boler with the original tail lights you know where I am coming from.

7" LED lights fit perfectly, just cut the wires off the original lights and connect to pigtails on new lights. LED lights must be connected with the correct polarity or they will not work.

Lights were bought at Princess Auto.

How To's & Info

Acorn Nuts On Pop Rivets

Boler Specs.

Cushion Templates

Door Sag Quick Fixes

Drawer Above Fridge

Hitches and Towing

Making a New Frame

Replace a Window Crank

Scissor Jack Levellers

Screen Door

Small Mods & Discoveries

Wiring and Batteries

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