Troubleshooting trailer ground (weak brakes)

[joshuabardwell]

Every time I hook up my trailer, I do a little "skid-test" on the brakes to make sure they're adjusted right. Yesterday, when I did that, they didn't pull very hard at all. I jacked the trailer up and applied the brake button on the controller, then spun the wheels by hand, and I could feel the brakes pulling a little, but not very much. I could still turn the wheels by hand, which I'm sure isn't right.

A little background. The trailer is fairly new. It has about 300 miles on it. When it ticked over 300, I adjusted the brakes, per manufacturer's recommendations. I adjusted the pads so they were just barely scraping the drums when the wheel was spun and no brakes were applied. Then the trailer sat for a while until I pulled it out yesterday to use it.

Another variable that's worth mentioning is that the truck I was using yesterday is a different truck than I have ever used the trailer on before, so I'm not 100% sure that the issue isn't in the truck.

Anyway, I checked voltage on the brake pin in the truck's connector and it was 12.5 volts with the brakes applied. Then I went on to checking ground and realized I don't 100% know what I should be looking for. On the trailer, there was about 2 ohms between the ground pin on the connector and the grounding screw that the brake disconnect battery uses (which is grounded to the frame of the trailer). On the truck, I wasn't 100% sure what to use as a ground. I tried the bumper, the hitch, and the ball, and got continuity, but different, wildly varying ohm readings. I'm not 100% sure it wasn't because my hand wasn't very steady with the test lead, though.

I have tried to find a concise set of troubleshooting steps, but everything I find just says, "Be sure you have a good ground." Okay. Can anybody give me any more details on how to do that?

PS: I haven't checked voltage at the brakes or anything like that because I got tired of being out in the sun and decided to work on it some more later.

 

[Diamondpilot]

A big issue I see is cheap undersized wiring going to brakes. For a tandem axle it should be 12ga min.

Chris

 

[joshuabardwell]

A big issue I see is cheap undersized wiring going to brakes. For a tandem axle it should be 12ga min.

I appreciate the input. I've never been sure how to measure the gauge of non-solid-core wire.

 

[Diamondpilot]

I appreciate the input. I've never been sure how to measure the gauge of non-solid-core wire.

Easy way is by code on the wire itself or just a pair of graduated strippers

 

[newbury]

just a pair of graduated strippers

My wife doesn't like it when I have a stripper, much less two, even if they did just graduate

 

[Depmandog]

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

All of the trailer functions i.e.. brakes and lightning need to ground back to the vehicle's ground.

I would hazard a guess that 90% of my "problems" with trailer electrics can be attributed to a poor ground, the other 10% to the pin connection.

Take some emory cloth and clean the rust from the ball and hitch tubing. Lubricate all of the surfaces with WD40 and then retry your connection. Also spray both connector ends.

This should solve any ground issues. As far as Ohms, etc...no idea. Any other adjust would then be from your controller.

 

[BobRip]

I would put a test light that loads up the ground and look for excessive voltage drop. This is a much better test than ohms test. When using Ohms on the low resistance scale the probe point of contact can vary in resistance a lot and give false readings as you have seen. With current flowing through the ground you will easily see varing voltage drops and probably one will stand out. Just to elaborate with current flowing check the voltage drop between the frame and the wire at the ground screw. I hope this is clear. You may be able to just turn on your lights and look for voltage drop on the ground.

 

[3930dave]

Good points raised above.... voltage (and drops) is often easier to assess than resistance.

(Ultimately, you may need to verify that 12.5 vdc on the 2 wires AT the brake pucks. To confirm that you are on the right pin, make sure that voltage varies with the manual test button/slider on your brake controller, if you have that type - don't leave it on manual test too long, some controllers don't like that).

For ground, if you can locate clean (no paint) solid metal on both truck and trailer, a quick test is to jump these two attachment points with a good battery jumper cable - parked of course, wrapping a jumper cable around your axle on the road is not fun, even less if it lands on somebody's windshield.

Best way to get a clean ground is to grind off any paint or rust, then install a stainless steel bolt through the frame. Coat it with grease (where it attaches to the frame) and you should have a good ground for quite a while.

Hitch ball will often give you a ground, but there are variables here - paint thickness on hitch frame, type of bolts/lock washers used, rust.....

(Gradiated strippers.... I'm thinking Jethro Bodine goes to college :laughing: !).

Rgds, D.

 

[jeffsw6]

There is a ground wire in the 7-wire trailer coupler, and if it isn't working, you should fix it. Yes, the metal tongue of the trailer should conduct electricity to the metal frame of your truck, but with a lot of painted surfaces in the way, etc. this can be unreliable. If the ground wire in the coupler doesn't work, repair it.

What is a good way to check this? I'm glad you asked. Jack the trailer up off the truck and make sure everything on the trailer still works without the vehicles touching each-other, except where the 7-wire coupler hooks up. If everything doesn't work, repair the ground wire in the coupler.

In case I was unclear, the ground wire in the coupler should always be functioning, and if it isn't, you should repair it. $0.02.

 

[joshuabardwell]

That is a good test--to make sure everything works with the trailer totally disconnected. Normally, I would test grounding by checking the resistance between the ground pin and a known good ground. But the challenge is finding a reliable source of ground near the plug. If everything works with the vehicle and trailer not touching, can I assume there's a good ground?

 

[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