Introduction: Trailer Light Tester

I have a few trailers now and keeping after their lighting is getting to be a pain. Bringing each one over to the truck to test it is a little inconvenient since I use a golf cart to store them around behind my garage.

I looked around and found some trailer light testers on the web but they look like pre war monsters and their prices range from $500 to $2,000. Luckily I have a good stock pile of salvaged laminate flooring to draw from and HarborFreight just sent me a coupon for their plastic ammo boxes on sale at $4.99 each. Now to check the electronics pile.....

I added a small voltmeter / ampmeter combo to monitor the battery status. That way I know when its time to recharge and I get a quick health check on the brakes.

Step 1: Making It Pretty

I have a bunch of laminate flooring pieces I salvaged from a friends kitchen remodeling. He pulled up the kitchen and hallway to replace it with tile. These flooring pieces can be seen in many of my projects on Instructables and i'm sure will be in many more.

It turns out laminate flooring engraves really well. Be careful around the dust. Some laminates contain epoxy or fiberglass fillers...

I use .3mm v bits on a 3040 CNC machine to engrave all the lettering. I set the depth to .025in and take that cut in one pass.

Once the lettering is done I switch to a 1/8 fluted bit to rough out the holes. I set my depth to .25 and my material is .33 so it doesn't cut through. I have tried using tabs and a sacrificial board but the extra setup time doesn't appeal to me. I'd rather zip out the pieces later with my Dremel.

When its all done I spray some flat black paint over the lettering then wipe the excess away with some WD40.

you can edit the layout on easel

Really nice looking. The edges are a bit rough since my saw needs a better blade. It also helps if you cut it with the good side down on the table...

Hard to believe people were walking on this stuff not too long ago....

Step 2: Assembly

First problem was the LED holders were the same depth as the panel. I had to remove a little material from the back side for the nuts to catch.... I made quick work of that with a 3/4 bottom cutting bit. Same bit I use to surface a sacrificial board when I make PCB's or Plexi engravings.

Once that relief was cut the assembly went pretty quick. I had a spool of red wire so that's what I used. Some of you may cringe at that thought of all the wires being the same color....

Just remember to install the flasher switch upside down. That way on is up for all switches. look at the schematic and it should become obvious why the flasher switch is that way.

  • 12V Lead Acid Battery (MCM Electronics 29-3120 $20.99)
  • D1 - D6 Blue LED (Tayda Electronics $0.05 each)
  • 6 LED Holders (Tayda Electronics $0.04 each)

  • 2 Fuse Holders 6x32mm (Tayda Electronics $0.49 each)

  • SW1 - SW5 SPST Rocker Switch (Goldmine Electronics G19473 pkg of 10 for $2)
  • SW6 SPST Momentary Switch (Tayda Electronics $2)
  • F1 20A Fuse (Tayda Electronics $0.45 each)
  • F2 15A Fuse (Tayda Electronics $0.45 each)
  • R1 -R6 1K 1/4 Watt (Tayda Electronics $0.01each)
  • 7-6-5-4-Way Trailer Connector(s) as desired (Auto Parts Store $5 - $50)
  • Tungsol 552 Flasher or equivalent (Auto Parts Store $2 - $12)

Step 3: Fitting the Battery and Other Pieces

I've had this battery floating around for a while now. It's a reject from my UPS but it will do to get this tested. There's just enough room next to the battery to add a cigarette lighter socket for charging the battery and powering accessories like my air pump and search light.

When it was all done the lid didn't close. Turned out the trailer connectors hinge was about 1/8 inch too tall. I fixed that with a Dremel and a power rasp bit....

Step 4: Using It

I chose to only add a 6 way connector. I have a LOT of leftover Velvac tractor trailer connectors so it's my choice for everything. I do have a couple of things like towing lights and a small utility trailer that have a 4 way connector but a 6 way to 4 way adapter makes quick work of that.

A quick test with that adapter and a cheapie led test plug says I got those 4 wires right....

I did add all 7 circuits to the schematic so you can use a 7 way if you want. Just add a wire from the 12V binding post to the connector. I would keep the binding posts even if you do use a 7 way since it's a great way to test replacement lights you get at yard sales.

A ground clamp from that black binding post to the trailer frame will let you test for a weak trailer ground...

You should turn on each circuit one at a time. This way you can see if one circuit is shorted to another. This happens a lot with the parking lights shorting to the signal wire in cheap trailer light sockets. Believe me that's something I know about.

Step 5: First Test, My 1/2 a Toyota Hilux Trailer

Everything worked perfectly. all lights work! I'm actually surprised by this since I used a LARGE sledge hammer and an impact gun to build this trailer....

This trailer is made from 1/2 of an old Toyota pickup and a diamond plate aluminum tool box on the front. The aux power lead is used to run the backup lights and the yellow lights though a flasher.

That way if I flip the switch in the cab I get backup lights as well as hazard flashers while not losing my regular signals and brake lights. There is a switch panel instructable out there too........

My Blazed is wired with a large 12V wire from the battery to the rear. Under the rear bumper is a relay box with a separate relay for each circuit. that way I never worry about a trailer light short affecting my main lights on the truck. I probably should do a separate instructable on that box...

Step 6: Second Test, My Harborfreight Utility Trailer

This didn't go so well. The tester worked great and every bulb works except the right signal...

That wouldn't seem so bad but this is my 3rd set of lights and I'm getting tire of these cheap lamp housings. I see a LED trailer Light instructable coming soon.

Step 7: Final Test for Today, My Tow Dolly

See my tow dolly instructable for more info but this beast gets a lot of use. Just last month my son called and said his car died on him. I went and grabbed his car and brought it home. This dolly is why I built this tester. The dolly has a 6 way connector that plugs into the truck and runs some clearance lights and the trailer brakes.

There is a 4 way connector on the dolly to plug in tow lights. Well, those lights wouldn't work. Luckily he was on a country road about 3 miles from home. No turns no stopping so those clearance lights would be good enough...

About stopping, That was the other concern. It felt a little weak... Well, that brake current shows only one brake is connected. I have the 12in brakes which draw 3 amps per wheel. That should be 6 amps....

If you have 10 through 12-1/4 in brakes its about the same. They all use 3.2 ohm magnets. The little 7 inch brakes use a 3.9 ohm magnet which draws about 2.5A per wheel. 11.9 Volts / 3.38 Amps = 3.5 ohms. About what I would expect with the harness loss included for one wheel.

I found that if I plug the towing lights into the tester directly they work fine. They just don't work off the dolly pigtail. Plus there's 8 bulbs in the clearance lights and 4 are out. I have to open the connector to see if any wires broke off in there. If not time to slit the whole harness open.

Looks like I have a lot of work to do now.......

Step 8: Upgrades

One thing it really needs is a current limiter. I may throw in an Auto PC power supply I have laying around. It would boost the battery voltage to a constant 15V and provide the current limiting needed, maybe. Sounds like too much work now that I typed it out. Maybe using a circuit breaker in place of that fuse holder would be good enough....

I will add the cigarette lighter socket for charging. I already added it to the schematic. And added one to my rear bumper....

Just need to pop a hole in the ammo case for it.

But then I came across a matching USB charger port.

And then I saw this dual one thats looks like a perfect fit for the front of the box...

I keep telling myself "you don't need it..."

I'll probably order it right after I post this Instructable.....

Reclaimed Wood Contest 2016

Participated in the
Reclaimed Wood Contest 2016

Sensors Contest 2016

Participated in the
Sensors Contest 2016