Troubleshooting trailer ground (weak brakes)

[jeffsw6]

If everything works with the vehicle and trailer not touching, can I assume there's a good ground?

Yes, absolutely.

I think your first guess about one of your trucks having a faulty coupler/wire is probably right.

 

[joshuabardwell]

Yes, absolutely. I think your first guess about one of your trucks having a faulty coupler/wire is probably right.

Okay, well, I just went and performed this test and everything seems to have checked out fine. Running lights came on and stayed on. Turn signals worked. Brake lights worked.

I also remembered that I have a four-pin connector hanging underneath my bumper, in addition to my seven-pin connector, which let me test the continuity between the truck's ground and the trailer's ground. I measured about 0.2 ohms between the ground pin on the 4-pin connector and the ground pin on the 7-pin connector, and about the same between the ground pin on the 4-pin connector and the grounding lug on the trailer, when the two were connected.

Conclusion: no grounding problem.

 

[joshuabardwell]

The battery on the trailer is a safety feature, a part of the breakaway safety braking. Measuring ground here will not tell you anything.

Sorry for the confusion. The battery system is grounded to a lug that is bolted to the trailer frame. This should be common ground with the rest of the truck/trailer system, right? That's the place I was measuring from.

 

[Travelover]

My opinion is to not use the frame as a ground. For another couple of bucks, you can run a second copper wire to the brakes and each tail light and be done with it.

 

[jeffsw6]

Sorry for the confusion. The battery system is grounded to a lug that is bolted to the trailer frame. This should be common ground with the rest of the truck/trailer system, right? That's the place I was measuring from.

Yes, the frame of both vehicles is your ground, and they are connected together by both the coupler, and the metal surfaces of the ball mount/etc if that path is not being interrupted by paint or rust. As long as one of those connections is good, your trailer ground will be good.

 

[horsepuller]

Electrical troubleshooting works best when testing for proper voltage under (electrically) loaded conditions (rather than ohms testing). I suggest you perform the following test. (From your last post I am assuming you have a VOM (volt ohm meter).)

Verify your original symptom - apply brake controller manually, move tow vehicle, and verify that wheels do NOT skid. Now for the test.

Run a jumper wire (any gauge will do) from the tow vehicle's battery negative terminal to the negative terminal of your your VOM. Put VOM on DC volts scale. Jack up your trailer wheels on one side. Apply the apply brake controller manually (and keep it on somehow). Get under the trailer axle area (use jack stands under the trailer) and probe the leads going to one of the trailer brakes, as near as possible to the drum area. You will need to pierce the insulation on the positive lead. Try a needle or pin if you do not have a sharp electrical probe. If the electric brakes have two leads, try one at a time. One will be the positive, one the ground.

You should see 10 to 12 volts on your meter. If not, more checks will be needed to track down the problem. If you see 10 to 12 volts, try turning the wheel in the normal forward direction of travel. If it turns, the electric brakes need work.

This is the best I can suggest. Please post your results and we can go from there.

 

[Diamondpilot]

I still say if you have voltage its undersized wiring not allowing sufficient current if the grounds are good and tight.

Chris

 

[joshuabardwell]

Thanks for the input. I will try these tests tomorrow--maybe not until after work. Stay tuned!

 

[ptgdigger]

Rust is another thing to think about, electric brakes work by energizing an electromagnet that is attached to a lever arm , when energized the magnet attaches itself to the inside of the drum face and creates a pull on the lever arm proportionate to the amount of drag from the magnets grip on the rotating drum, any rust that develops on the magnet path in the drum can lessen the drag and therefore lessen the braking action, usually this flash rust will wear off pretty quick and braking will get stronger.

Also you said this isn't your normal tow vehicle , there could be enough difference in the performance of the vehicle brake controller to notice, all brake controllers have some adjustment for "gain", using the trailer brake actuator on the box will bypass the gain adjustment, so doing the "skid check" should have eliminated that variable.

Ray

 

[RobertN]

On my 5th wheel, when I found the "T" for the in-bed connector only had one ground wirre but the truck has two.

I found at full trailer brake controller voltage, I should have had 12V+/- at the brakes. But, I only had about 6V at best.

I still say if you have voltage its undersized wiring not allowing sufficient current if the grounds are good and tight.

Chris