Truck and Trailer wiring tester

[Dave27]

How exactly would that test a trailer?

On the trailer, I use the multimeter to test continuity on each circuit. On the truck side, I have someone hit the brakes and I can test voltage across that pin and the ground. Similar for the lights and turn signals. it's pretty straightforward.
Dave

[RPAspey]

I made a test box to check the trailer with some switches, a flasher and test plugs for checking brake load. no battery is needed as on the trailer 12v is already on the 7 pin. I'll try to dig up a picture of it.

BTW, I use a DC ammeter across the test plugs to apply 12v to the brakes. I can then check the current that all 4 magnets draw in total. If one is bad, the load drops by 25%. For the life of me, I can't remember what full load value is right now, but I have it written down.

Here's the pix of my tester.

[Jkwilson]

On the trailer, I use the multimeter to test continuity on each circuit. On the truck side, I have someone hit the brakes and I can test voltage across that pin and the ground. Similar for the lights and turn signals. it's pretty straightforward.
Dave

Continuity isn’t going to tell you much about whether lights work, especially with LEDs. A short has continuity.

[Jlawles2]

Here's the pix of my tester.

That's a nice looking tester. Did you put a flasher relay on the turn signals so they flash when testing? The only other thing I might consider is adding a couple of lights so I can ensure the tester is working and providing the signal.

[RPAspey]

That's a nice looking tester. Did you put a flasher relay on the turn signals so they flash when testing? The only other thing I might consider is adding a couple of lights so I can ensure the tester is working and providing the signal.

Thank you.

I used a flasher specially for LED lights. With the test jacks, I can test for 12v present from the battery. It also confirms the ground. Other than that, the rig lights prove it works.

[Yoda]

Here's the pix of my tester.

Can you post a picture of the back and the wiring layout? Looks like an easy build.

[TravelHabit]

First step is to ensure the truck is sending the correct signals. Then its just a matter of plugging the trailer in and checking the trailer lights. Brakes are trickier. I've done that by putting a compass by each trailer wheel. If the compass changes direction the brakes are energized. More complicated is something like this: testing-trailer-brake-magnets-for-proper-function

A couple of years ago I made my own tester:

The cord is long enough to allow me to see it from the drivers seat .

Its very simple to make. Just need to get some 12V LED lights (like these www.amazon.com) a 7-way cord plug connector (amazon) and connect the appropriate wires (see attached pdf wiring diagram).

Note that the left brake is not a LED, it is an actual brake bulb. The reason for this is that it allows one to see the amount of braking the controller is providing. Brightest is full brakes with dimmer values for less and less braking (i.e. voltage). On my brake controller I have a knob that adjusts this and I can see brightness change as the knob is turned.

I didn't even solder the connections!

[Jkwilson]

First step is to ensure the truck is sending the correct signals. Then its just a matter of plugging the trailer in and checking the trailer lights. Brakes are trickier. I've done that by putting a compass by each trailer wheel. If the compass changes direction the brakes are energized. More complicated is something like this: testing-trailer-brake-magnets-for-proper-function

A couple of years ago I made my own tester:

The cord is long enough to allow me to see it from the drivers seat .

Its very simple to make. Just need to get some 12V LED lights (like these www.amazon.com) a 7-way cord plug connector (amazon) and connect the appropriate wires (see attached pdf wiring diagram).

Note that the left brake is not a LED, it is an actual brake bulb. The reason for this is that it allows one to see the amount of braking the controller is providing. Brightest is full brakes with dimmer values for less and less braking (i.e. voltage). On my brake controller I have a knob that adjusts this and I can see brightness change as the knob is turned.

I didn't even solder the connections!

I wish I had a picture of the setup I built for a local trailer dealer 20-ish years ago. We took a steel shop cart and mounted a full set of trailer lights on it Stop/Turn/Tail as well as marker and backup lights and a set of 4/6 selectable brake magnets. Test points in the circuit for voltage and current. Lawn mower battery with charger on board with a switch panel to test the trailer. 4, 5 and both style 7-pin connectors on each half. Ground leads to verify the frame ground on truck and trailer. His crew loved it. Roll it up to a customer’s truck and know quickly if it was a truck or trailer problem. Then use it to isolate the trailer problem.

Sadly, the guy I built it for passed away, and the new owners trashed it because nobody was left that knew how to use it.

[RPAspey]

Can you post a picture of the back and the wiring layout? Looks like an easy build.

Here's a wiring diagram. I recreated it as I lost the original diagram many many years ago. I hope it helps.