KQ6XA Bonnie Crystal
Standard Connector System
for Portable Lighting and Electronics
by Bonnie Crystal KQ6XA
Battery PacksRadio Transceiver2 Wire Trailer Plug ConnectorsHeadlampCommonly Available ConnectorsSolar PanelElectronic Equipment Plugs
Commonly available plug has many uses for DC Powered Equipment.
This is a standardized modular system based on using "2 Wire Trailer Plug Connectors"
which are available almost universally in automotive parts and radio electronics stores.
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Battery Powered Applications :
Caving, Backpacking, and Climbing Headlamps, Camera and Video Equipment, Radio Transceivers and Cell Phones, Mobile 12 Volt Electronic Equipment, Solar Powered Systems, GPS Receivers, and Portable Computers
Complete Battery Lighting and Communications Package 
1. Complete Battery Lighting and Communications Package
Basic Plug Connectors as Purchased   
2. Basic 2-Wire Trailer Plug Connectors as purchased in the store.  
The wires are simply cut in the center when building the system.  
For DC Power systems (includes all battery systems),  
The BLACK is NEGATIVE!  
In this photo, the BATTERY PLUG  is on the LEFT.  
EQUIPMENT  PLUG is on RIGHT.
Battery Pack Being Assembled With Plug and Fuse
3. A 6 Volt (4 D-Cells) Battery Pack Being Constructed.
Note BARE SIDE of plug is BLACK wire for BATTERIES!
Completed 6 Volt Battery Pack With Plug and Fuse
4. Completed 6 Volt Battery Pack with Plug and Fuse.
Fuses may not be desirable in some applications, or with AA battery packs. The fuse is to prevent draining of the battery in the event of a short, and to protect electronic equipment. Generally, caving headlamp battery packs are not fused.
Gaffers or duct tape used to hold the wires and D-Cells securely.
Note: BARE SIDE of Plug is BLACK wire for BATTERIES!
Petzl Duo Headlamp Modified With Plugs
5. Petzl Duo Headlamp Modified with Plugs.
Remove batteries from pack.
Cut cord in half and strip ends of wires. 
Check polarity of wires with a continuity meter.
Connect trailer plugs in between. Wires are secured with electrical tape.
Note: BARE SIDE of plug is BLACK wire for BATTERIES!
Modified Petzl Duo Mounted on Helmet
6. Modified Petzl Duo Headlamp with Trailer Plugs.
Note the plugs tucked under elastic headband when mounted on helmet.
Trailer Connector and Radio Transceiver Plug Adapter
7. Trailer Connector to Radio Transceiver Plug Adapter. 
12 or 6 Volts.
Icom Handheld Transceiver With Trailer Plug Adapter to 6Volt Battery Pack
8. ICOM Handheld Transceiver Connected to 6Volt Battery Pack.
Scorpion Multiple Plug Adapter
9. "Scorpion" Multiple Plug Adapter for running 3 pieces of equipment from a single battery pack source.
Connector on LEFT plugs into the BATTERY.
3 Connectors on RIGHT go to the EQUIPMENT.
Solar Panel Charger With Trailer Connector
10. Mini Solar Panel for charging battery. Note this is a special case of polarity because this is a battery charger. To keep the polarity correct, the black wire side of the plug is not bare. This is so that the color matches to the black bare side of the battery's plug
12 Volts.
Electronic Equipment with Plug Attached 
11. Radio Equpment with plug. 
Voltage should be clearly marked on all sensitive equipment. 12 Volts. 
Cig Lighter Plug Adapter 
12. Cig Lighter adapter cord. Note clearly marked plugs. 
The "charge battery only" plug should be insulated with tape when not in use. 
12 Volts. 
 
9 Volt Battery Adapter Cable 
13.  Battery Clip 9 Volt adapter.
Gel Cell Rechargeable Battery with Plug 
14. Gel Cell Rechargeable Battery. This one is two 6 Volt batteries in series, making 12 Volts. A fuse connects between the two cells.
Battery Substitute Plug for Compaq Laptop 
15. Battery Substitute/Plug for a Compaq Laptop Computer. 
Old NiMH batteries have been removed, a small hole is bored in the side of the pack, and the wires are soldered in place.
Extension Cord 
16. Extension Cord. Several of these are handy for all equipment, especially headlamps.. 
This one is 4 feet long. Use lamp "zip" cord or cable. Suggest 16 guage or larger to prevent voltage drop.
GPS Receiver with Plug 
17. GPS Receiver with Plug. 6 Volts.
Portable Computer with Modified Battery Substitute 
18. Portable Computer with Battery Substitute/Plug. 
The Ni-Cad batteries are removed from an old worn-out pack.  
A plug is then wired into the pack by soldering. 6 Volts. 
Radio Transceiver with Plug Attached 
19. Cave Radio Transceiver (185kHz SSB/CW)  
with Plug. 
12 Volts. Antenna Not Shown.
Icom Handheld Battery Substitute/Plug 
20. Battery Substitute/Plug for ICOM Handheld Transceiver. 
The Ni-Cad batteries were removed from a worn out pack, and plug wires are soldered in place. 6 to 12 Volts.
Connecting Equipment to Plugs 
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To connect plug wires permanently to electronic or lighting equipment, select a plug which has the black wire to the insulated side of the plug. Then simply strip about an inch of  insulation off the end of each wire, twist the appropriate wires together, and secure with electrical tape. This connector lends itself to field repairs and also connecting just about anything by simply inserting wires into its openings and taping them in place. For plugs such as those used on transceivers and other electronic equipment, the trailer plug wires are soldered directly to the appropriate type of plug. See example in photo 7.
Durability and Strain Relief 
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The Simple 2-Wire Trailer Connector has been used for many  years in the automotive industry and is extremely durable---even cave-proof. Still, care should be taken not to pull on the wires when the connectors are being un-plugged, especially the first few times the plugs are inserted and removed, until they start to loosen up a little.When in use, especially for headlamps and battery packs carried in rough environments, it helps to use tape to secure the cord on each end so that there is not a direct pull on the plug wires at where they enter the connector. 
There are 2 basic rules to remember when hooking up this system:
1. BLACK WIRE is NEGATIVE.
Most brands use red and black wires, but some use white and black wires.
Always match black to black when plugging equipment to battery packs.
2. BATTERY NEGATIVE is BARE.
When building the system, connect all battery power sources using the black wire
of a plug which has the bare side of the connector to the black wire.
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CAUTION: If the simple rules are followed, the system is completely interchangeable, and polarity of positive and negative is preserved. When plugging in, always match black wire to black wire. Keep in mind that battery packs can be built using any voltage. It is always necessary to verify the required voltage matches the equipment being used before plugging in!The most common battery systems being used are 6Volts and 12Volts.
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DISCLAIMER: This web page is intended for educational purposes. No liability is assumed on behalf of the author for stupidity or lack of expertise on behalf of the user when hooking up systems.
 
Other Applications for the Trailer Plug Connector
Field Phone Wire Spool with Plugs 
Spool of Field Phone Wire with Plugs Attached. 
Courtesy of Walt Pirie.
This application for field telephone wiring was submitted by Walt Pirie. It is a spool of surplus comm wire, as frequently used in cave rescue applications, with a handle. 

Walt writes:"Another useful application of these connectors. The VPI Cave Club uses them on its field phones for cave rescue. There's one attached to the phones. One is wired at at each end of every spool, and a spare one taped below it. The spare one has bare wires on the other end. That way it can be plugged into the attached one leaving the bare wires for attaching to wires from other groups that don't have the connectors.---Walt "

Author's note: 
Careful checking of polarity when building this might help it to be used as a long extension cord in the field. Although, some voltage drop will be encountered, depending upon how much load is used. Field Telephones are capable of producing over 100Volts AC when the ringers are used. Don't plug your GPS into this :-)  ---Bonnie
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The author and producer of this web site is Bonnie Crystal KQ6XA.
It may be reproduced freely provided credit is given to the author.
Copyright 1999 Bonnie Crystal
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