How to test trailer lights

How to test trailer lights

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How to Wire the Navigation Light of a Basic Boat

How to test trailer lights

How to Hook Up a Marine Voltmeter

Boating at night means that, if a boat is less than 65.6 feet long and is not a rowboat, it must display navigation lights. On recreational boats, this means a combination (or bi-color) bow light with a red lens to port, a green lens to starboard and a white stern light. Although all manufactured boats come so equipped, the do-it-yourself sailor will have to wire these lights into his boat’s electrical system in a manner that will pass muster should his boat be inspected. They should also be wired in a way that will alert the sailor should the bulbs burn out, so that they can be quickly replaced.

Items you will need

Combination bow light

Toggle switch with an indicator bulb

Waterproof wire connectors

Basic hand tools

Soldering gun and silver solder

Drill mounting and wiring holes for the bow light unit, using the template provided with the unit to mark the holes on the hull of the boat. Repeat the procedure for the stern light. Neither the bow nor stern lights can be obscured by any part of the boat, and they should be as far forward (for the bow light) and as a far aft (for the stern light) as practical.

Decide on the route the wiring for the lights should take. If necessary, fish the wire for both the bow and stern lights, and the wire from the stern light to the control panel, through walls, under decks or under the curve of gunwales to prevent tripping hazards resulting from the wires. As you fish the wires, mark each with with colored electrical tape, one color for the line from the battery to the bow line, one color for the wire from the bow light to the stern light and one for the stern light to the control panel.

How to test trailer lights

Schematic of wiring the bow and stern lights

Attach one end of the wire for the bow light to the positive terminal of the battery or a bus bar connected to the battery. Attach the other end of that same wire to the red wire of the bow light with a waterproof wire connector. Like the marine VHF radio, the navigation lights should be on an isolated circuit. Attach the black wire of the bow light to the wire leading to the stern light with a waterproof wire connector.

Attach the red wire from the stern light to the wire leading from the bow light with a waterproof wire connector and attach the black wire of the stern light to the wire leading to the control panel, also with a waterproof wiring connector. At the control panel, attach the wire from the stern light to one of the terminals on the toggle switch with a soldered connection. Connect the other terminal of the toggle switch to the fuse holder with a soldered connection. Finally, connect the unattached end of the fuse holder to the negative pole of the battery or the bus bar.

Test the lights. If either the bow or stern light is inoperative, the indicator light on the toggle switch will be dark. Even if the indicator light illuminates, check the navigation lights visually as well. The lights are wired in series so that should either light become inoperative, the indicator light on the control panel will warn the boater. Secure the bow and stern lights permanently in place and lock the toggle in place on the instrument panel.

Trailer lights and wiring are exposed to rain, snow, salt, road dirt and grime. The wires and bulbs are subject to chaffing, corrosion and damage. The bulb sockets and ground connections are particularly prone to corrosion.

How to test trailer lights

Trailer lights must be tested often for everyone’s safety in traffic and to avoid legal and regulatory citations and fines. Testing trailer lights takes time and time costs money.

Testing trailer lights normally requires a towing vehicle connected to the trailer then walking back and forth from the vehicle to the back of the trailer to verify that all the trailer lights function properly – left signal, right signal, brake lights, tail and clearance lights. A second person could be in the vehicle to operate the lights. But that is double time consuming and very expensive for a business with a fleet of trailers.

How to test trailer lights

Because of the hassle, time and expense, most people don’t test their trailer lights in advance. Instead they wait until they are hooked up and do a quick walk around to check the trailer lights then realize they have a problem. But everyone is ready and anxious to go, so off they go traveling or to the job site traveling illegely and not safely. This could result in traffic citations or possibly a much more expensive traffic accident.

What do customers say about Light Check

Light Check has made trailer light checking a lot easer. I check them alone most of the time. It’s like having a second person helping.

I do a lot of D.O.T inspections. With Light Check as a tool has made my job more efficient.

Light Check makes it easy to distinguish between vehicle or trailer wiring problems.

It has saved us a lot of time

When I rent out a trailer, sometimes the lights do not work when hooked up to the customers vehicle. I connect Light Check to the trailer and show the customer that the lights on our trailer are working fine. This has helped significantly with customer relations.

Light Check is a self-contained, portable device that connects to the wiring connector of the trailer. It includes a 12-volt internal rechargeable battery, electronic diagnostics for light circuit analysis, ground wire, battery charger and instructions.

Simply connect Light Check to your trailer wiring, turn on the power and press Select button for Cycle. Light Check will continue cycling through each of the trailer light circuits in 5 second intervals allowing one person to easily check the signal lights, brake lights, tail and clearance lights without a towing vehicle or second person to assist.

Use the Select button to operate any individual circuit continuously for over current (short circuit) and low current (open circuit). If a problem is detected, LED fault lights will indicate the type and source of the fault.

Save time and money, reduce fines and penalties by testing your trailer lights with LIght Check.

  • Increase safety for your family, employees or customers with properly operating trailer lights
  • Test trailer lights in 5 minutes or less.
  • Reduce payroll costs with one person operation and no vehicle to hook-up
  • Prevent traffic citations and fines

Simple yet comprehensive

  • Self contained with internal rechargeable battery
  • Electronic diagnostics indicates the type and source of faults when problems are found
  • Unique Cycle mode cycles through the light circuits for simple one-man operation. Tests signal lights, brake lights, tail and clearance lights in repeating cycle.
  • Individual circuits may be operated continuously for trouble shooting or repair

Simple to operate

  1. Connect Light Check to trailer wiring connector
  2. Turn the Light Check power switch to ON
  3. Press the SELECT button once for Cycle
  4. Test and observe lights for proper operation
  5. Turn the power switch to OFF when finished

With no hook-up vehicle or second person to assist

trailer light test tester check checker diagnostics repair maintenance trailer wiring diagnose problem tool trailer lights troubleshooting

One of the most complicated things to test on a car often seems to be the 7-pin trailer plug as it hosts 7 different electrical connections in one plug/wire.

But with the use of a simple multimeter with a black/red probe you can test this easily at home to determine if there is an electrical break within the plug.

What will you need?

We recommend using Innova 3340 for this task

You’ll need the following items in order to test it effectively:

  • 7-Pin Trailer Plug
  • Running Vehicle
  • Multimeter with black/red probes that can test for volts
  • 2 people – one to run the vehicle and one to run the multimeter
  • Replacement Light Bulbs (Optional)
  • Sandpaper (Optional)
  • Electrical Contact Cleaner (Optional)

The configuration of the 7-pin Trailer Plug

The 7-pin trailer plug is complicated because it hosts 7 different connections all in one (watch the video right below this paragraph).

You may have other types of plugs which have 3, 4, 5 or 6 different connections but for this one, I’ll focus on the most common 7-pin plug.

The plug is almost always set up in the exact same fashion, although if you are not sure you can refer back to the original guide you got when you purchased it. A typical 7-pin plug will be setup in the below fashion:

  • Top right = 12-volt hot lead
  • Middle right = right turn/brake light
  • Bottom right = brake controller output
  • Bottom left = ground
  • Middle left = left turn/brake light
  • Top left = tail and running lights
  • Center = reverse lights

If you are not sure which is which, I will also show you below how you can find out using your multimeter.

How to Test 7-Pin Plug with a Multimeter

To test if any of the wirings in the 7-pin plug is not working you will need to use your digital multimeter and ensure it is capable of testing for volts.

Turn your multimeter to the V symbol on a multimeter dial.

Next, insert your black lead into the COM port and your red into the voltage port.

  1. When your multimeter is set to test volts, you’re ready to start. You can insert the black probe into the bottom left slot of the 7-pin plug as that is the grounding wire. Insert the red probe into the top right slot of the plug. If you are getting a reading near to 12 volts then it means that electricity is flowing in and out of the plug normally. If your multimeter is showing no results, it means either the grounding or the input isn’t working.
  2. Now to test each of the lights to determine if any of the wirings for each light isn’t working you will leave the black probe into the grounding slot of the plug. You can then move the red probe into the first light slot – let’s pick the middle right slot in the plug for the right brake light.
  3. Ask the person assisting you to then press on the brake light. If the pin wiring for that is working correctly you should see 12 volts appear on your screen. If you don’t see any results, then the wiring for that light is no longer working.
  4. If it is working, then you can simply move the red probe to the next slot in the plug and test each of the brake lights, blinkers, and reverse lights until you’ve eliminated any of them as issues.

Additional Troubleshooting

If you have a specific light burnt out and you’re not sure what is causing it, testing for continuity is one thing you can do, but there are additional tests you can do that may help restore power to the circuit.

  • Clean the connector plug using an electrical contact cleaner to help ensure the plug is free from dirt and dust. You can use a brush to clean out the inside contact pings to ensure it’s clean which often can cause a disconnect in the circuit.
  • Check the ground wire to see that it’s connected tight enough to the metal frame of the vehicle. If it’s loose or not connected to the metal it may not be getting grounded which can cause your circuit to be broken.
  • Replace the bulbs which are not working as it may only be a faulty bulb and not an issue with the 7-pin plug. This is often the first thing you should do as it most commonly will be a burnt-out bulb.
  • Sand away corrosion on the sockets which can often occur from water getting into the socket. You can use sandpaper by rolling it around a metal rod and connecting it with tape or glue. Then insert it into the socket and grind out any corrosion.

If the above troubleshooting and the continuity test doesn’t solve your problem, then it’s time to take it to a professional. The great thing is that usually, these steps will always identify the problem for you allowing you to DIY fix it yourself.

Suggested Multimeters

There are many great multimeters on the market, but I have my own personal favorites which are perfect for automotive uses:

Innova 3340: This Innova multimeter is one of those all-around good multimeters but specifically it’s great for automotive uses as it can test both volts and amps, plus temperatures, continuity, and much more.

It is also a very affordable multimeter which makes it easy to get for home use (Check price on Amazon).

How to test trailer lights

No matter what type trailer you own or operate, it is important to keep its signal lights in good working order.

Step 1

Plug your truck’s wiring harness into your trailer’s wiring harness and have an assistant get into the cab of your truck to test the lights. Test brake lights, left and right turn signals, hazards and reverse lights.

Step 2

Take note of which bulbs are not working.

Step 3

Remove the lens cover on the light or lights that are not working with a screwdriver.

Step 4

Remove the bulb or bulbs that are not working by pushing them in and twisting them to the left. Inspect the bulb at first to see if it appears to be burned out. If you have a working bulb handy you can plug it in to see if that solves your problem. If the new bulb doesn’t work, proceed to next step.

Step 5

Turn on your voltmeter and place the voltage setting at 20 volts.

Step 6

Place the negative (black) meter tester lead on the frame of your trailer to establish a ground.

Step 7

Place the positive (red) test lead against the bottom of the bulb socket. Do not allow the test lead to touch the bottom and side of the bulb socket at the same time because this can cause a short.

Note the reading on your meter. It should read 12 volts. If it does not read 12 volts it means this socket or its wiring is bad. Remove the wire from the bulb socket. Place one the negative test lead on the trailer frame and the positive lead on the end of the trailer wire. If the wire tests okay, it means the the wire works, but the socket is bad. If the wire is bad, both it and the bulb should be changed out.

How to test trailer lights

You’ve connected the trailer to the vehicle, but the turn signals and brake lights don’t work. You don’t know if the wiring is bad or you have bad bulbs. One way to troubleshoot the voltage on the connector plug is to use a circuit tester. On a four-prong plug, one prong connects to the right turn signal, one to the left and one to the tail lights. One is the ground. You will need a helper to operate the controls of the vehicle while you check the voltages with a circuit tester.

Step 1

Tell your helper to turn on the ignition while you go to the connector plug. Connect the alligator clip on the circuit tester to a metal part of the vehicle.

Step 2

Tell your helper to turn on the right turn signal. Place the probe of the circuit tester into the connection that has the green wire. The light on the tester should blink on and off.

Step 3

Tell your helper to turn on the left turn signal. Place the probe of the circuit tester into the connection that has the yellow wire. The light on the tester should blink on and off.

Step 4

Tell your helper to shut off the turn signal and step on the brake. Check the green and yellow connections again. The light on the tester should stay on for both.

Step 5

Tell your helper to release the brake and turn on the lights. Place the probe of the circuit tester into the brown wire connection. The light should stay on.

Tell your helper to turn off the lights and shut off the ignition.

2015 2500 dodge truck can not locate the fuse. changed out any fuse that reads trailer . brake and signal lights work fine. trailer parking light fuse.

Since you have changed out any blown fuses related to trailer lighting in your 2015 Ram 2500 I suggest you test the truck wiring without the trailer connected. This will help you isolate the problem to either the vehicle or trailer side.

Please refer to the linked photo (and article on trailer wiring) which shows the function carried on each pin of a 7-way vehicle socket. Running light power is carried on the 7-way contact at the 11-o-clock position as you look at the socket from the back of the truck.

Use a circuit tester like # 40376 to test the pin for a signal when the truck lights are on. If you do not detect a signal check for corrosion on or inside the socket. Also check the main wiring harness ground wire that attaches to the frame to ensure it is attached to a clean bare metal spot that is free of rust, undercoat, primer and paint. The ground must be made to clean bare metal in order to be able to pass all the power for the trailer lights.

You can also test the trailer directly, when it is not connected to the truck, by applying power directly from a well-charged battery (a spare or the one in the truck) to the ground and running light contacts on the trailer plug (again, please refer to the linked article). If the lights do not work even when fed this direct power then check the trailer’s main ground just the way you did on the truck and also inspect its plug for any signs of internal corrosion within the plug housing. If a new 7-way plug is needed we offer them in several lengths, such as # H20046 which is 8-feet long.

How to test trailer lights

Testing trailer lights after replacement of a lamp or a complete re-wiring job generally requires connecting the trailer to the tow vehicle. This can be a pain if the trailer is in the shop, or you’ve loaned your truck to your buddy for a short period of time. In just a few minutes and with very little effort, you can make a homemade trailer light tester with its own battery and trailer connector and check those lights anywhere.

What you’ll need

You’ll need a 12-volt battery, an inline fuse holder and 20 amp fuse, a tow vehicle-side trailer connector, some 14 or 16 gauge automotive wire, a two-prong turn signal flasher and a center off double throw toggle switch. You’ll also need a container such as a milk crate to hold everything. You can use any 12-volt battery, but for portability’s sake a lawn mower or motorcycle battery is best.

Wiring your tester

Start by connecting the inline fuse holder to the positive battery terminal. Connect the green wire from the trailer connector and a short length of automotive wire to the opposite wire from the fuse holder. Connect this short piece of wire to one of the prongs of the turn signal flasher. Using solderless connectors makes this job easy as a female spade-type connector fits the flasher prongs perfectly. Connect the other flasher prong to the center terminal of the toggle switch using a short length of wire. Then connect the yellow trailer connector wire to one side of the switch, and the brown trailer connector wire to the other. The final step in the construction of your trailer light tester is connecting the white wire from the trailer connector to the negative battery terminal.

Using the tester

Testing trailer lights with your new tester is easy. As soon as the trailer is plugged into the tester’s trailer connector, the trailer tail lights and any side marker lights will illuminate if they are functioning properly. Flip the toggle switch lever to one side to test the turn signal bulb. Flip the switch in the opposite direction to test the light on the other side of the trailer. This also tests the brake light because the turn signal and brake light uses the same filament of the bulb.

Electric trailer brakes must be controlled by a brake controller mounted in the towing vehicle within easy reach of the driver. This allows quick and easy adjustments to the controller to provide for different levels of brake application for varying trailer loads. This adjustment regulates the voltage available for the electric brakes; higher voltages apply the brakes more firmly than lower levels do. A sudden loss of the ability to modulate the level of brake application may indicate controller failure. Testing for this problem is well within the ability of most weekend mechanics, and requires a minimum amount of equipment.

Step 1

Press down on the brake pedal while watching the brake controller. The display on the controller should light up and hold a relatively steady reading, which should not vary by more than 1/10 of a volt up and down. It may be necessary to turn the ignition key to the “On” position for this step.

Step 2

Check the fuse to the controller if the display does not light up. Replace the fuse if it is burned and repeat the test. Another burned fuse indicates a short circuit that must be found and repaired before further testing of the controller can be done.

Step 3

Go to the trailer connector on the back of the tow vehicle with your multimeter. Have your helper hold down the brake pedal while you probe the terminal that is connected to the blue wire in the connector; in a properly wired connector this wire is the brake control wire and will have voltage present when the tow vehicle brake is applied. The amount of voltage present will vary as your helper moves the adjustment control on the brake controller. No voltage, or a voltage that does not vary, indicates a faulty controller or a problem with the blue wire itself.

Test for a problem with the blue wire by probing for voltage in the blue wire at the back of the controller. A lack of voltage here, or a voltage that cannot be modulated, indicates a failed controller.