The aim is to gain knowledge of and experience in trailer wiring and trouble shooting. In the process students should confront learning experiences that will expand their knowledge and understanding of: the notion of current flow in a circuit the concept of open and closed circuits the function of resistors (globes) to limit current the practice of using a common earth -the chassis.  

Techniques for locating and identifying the various circuits

Techniques for setting and using a multimeter - ohm-meter and voltmeter

 Extension work could include calculations with OHMS law concerning -alculations and measurements of EMF,Current, and Resistance (E = IxR), and Llso calculations concerning Power in a Circuit using the formula W = ExR :or Watts, EMF, and Resistance. Functions and calculation of fuse size, 7ating and type (quick-blow/slow-blow) could also be included.



Construct a CIRCUIT TESTER from the Kit for use in the exercise, then using either a trailer or a workshop model:

1. remove all wires to the plug and remove it from the wiring system

2. identify the circuits in the socket using a voltmeter and record them on the handout sheet.

3. identify each circuit in turn in the trailer wiring system eg. stop light, tail light,L/H & R/H turn etc.

4. connect the wires to match your diagram on the handout sheet

 5. test all trailer lights. Trouble-shoot as necessary. The exercise is more demanding if all the wires in the trailer circuits are t:he same colour.

 ALTERNATIVELY Have a devious student create deliberate aalfunctions in the trailer circuits eg. remove a bulb; loosen the earth iire; take some wires off; connect some wires to the wrong terminals; ,reate a short circuit (but be prepared to blow some fuses) etc.

1. test the function of all circuits

2. trouble-shoot and rectify as required

 There are a number of different Kits available for CIRCUIT TESTERS ranging from 3 or 9volt with battery, to one that indicates EMF in a wire ind indicates polarity.


  Components in Kit:
 1 x 7 Pin Utilux Base
 I x RCA Plug & Socket
 1 x 3 Pin Flasher Unit
 1 x Panel Mount Fuse-holder W/ 10 Amp Fuse
 5 x Toggle Switch
 1 x 12V Red Bezel w/ hook-up wire
 Insulated Wire (black /red /other)
 3 x Terminal connectors for flasher unit (insulated crimp)
 Cable ties

 Components in Kit:
1 x 7 Pin Utilux Plug
1 x 12V Tail/Stop Light Assy.
2 x 12V Amber Trailer Turn Light Assy
Eye Terminal w/fastener - Crimp type for chassis earth.
Insulated Auto Flex (usually one colour, but this)
  can be varied
5 x Cable Ties

1. Select a suitable panel and wire the controls and components into
the circuit as the wiring diagram indicates.
2. Wire the Trailer Base (socket) as the instruction sheet shows to maintain a standard system. Fix the Base in place and use the Cable Ties to harness the wires in the control panel.
3. Fabricate the trailer to your needs and mount the lights. The mounting screws form the earth connection for most trailer light assemblies.
4. Run wires, preferably all the same colours, from each light,
along the chassis.
5. Fix the machine screw to the chassis with a nut. Bare the end of a wire and crimp the eye terminal to it. 'Fit the eye terminal to the screw and tighten a second nut onto it to make a good contact. This wire is the common return earth wire.
6. Attach the trailer plug as per the diagram.
7. Tie up the wires with the cable ties.
8. Connect a 12 VOLT supply to the power lead into the control panel
and test the function of each circuit.


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