What is normal resistance reading for 5er brakes?

I found a guy with a truck like mine - his didn't recognize the trailer either. My truck recognized his just fine. Obviously the trailer.

Anyway, there were 3 (really THREE) broken wires on the axles. I must have hit something on the road to take them out.

Ohm reading 1.2 after the fix.

Start by pulling your breakaway cable and see if each wheel locks.

joebedford wrote:
My 5ers brakes aren't working. Trying to figure out if it's the truck (2011 Silverado HD) or the trailer (Voltage 3950).

While doing continuity checking of the cables and connectors, I disconnected the two leads that go from the cable junction box (on 5er) to the brakes. I got 3.3 ohms. Is that normal for a tri-axle?

If you have 7K axles with 4 brake drums 1 ohm would be reasonable. Each magnet would be about 4ohms with 4 in parallel to end up with 1 ohm. Of course there is a little resistance in the wire going to the magnets. My 4 magnets in parallel measure 1.1 ohms at the plug. With 6 magnets in parallel you should measure approx. .7 ohms.

Joe, I have a 2500 Duramax/Allison and had the problem with my trailer brakes suddenly quit working. There are four pages of my troubleshooting on the "Diesel Place." You may want to read them. I did use the "headlamp test," and it does work.

The one thing it will tell you is whether your problem is with the trailer or with the truck. I bought the headlamp from a wrecking yard and made up the "tester" myself.

Here is a link which I hope will work:

My thread on the Diesel Place

There a lot of "dead ends" and false starts on this thread, but it did turn out to be helpful. The poster "HeyMcCall" was the one who was on target about this tester. Note his responses.

A couple of open coils will increase resistance.

Joe, the magnet resistance should be between 2.5 and 3 ohms per magnet. The voltage at the axles should be between 9 and 10.5 volts. The current used at each axle should be between 5.6 and 6.6 amps.

All these numbers are dependant on wire resistance,corrosion, dirt, shorts,opens,if you are connected to the tow vehicle, if the motor is running.

If you are reading 3.3 ohms, you may be reading only one magnet (and it"s associated wiring), suggesting that the rest are not connected.

I would get a friend to help me try the compass test first to find out which magnets are being actuated, then voltage tests, current tests, and finally resistance.

I've been rethinking the resistance calculation I wrote about above. Where I did the measurement, I would see the full current draw from all brakes - 6 x 3 = 18amps. The would imply a resistance of 12V / 18amps = .66 ohms. I got 3.3 ohms.

Maybe the problems is the trailer. I'll find out of someone will let me plug in their 5er.

How could I get a higher, but not infinite, resistance??

Yes, it's a factory brake controller that has been working for 4 years. Silverado 3500HD. It doesn't recognize the trailer. I'm going to ask if there's someone at this campground who might be willing to let me plug their trailer into my truck. That should isolate it to TV or TH.

One comment about applying a full 12VDC when pushing down the brake pedal or moving the slide switch. I doubt the brake controller will ever send 12VDC to the trailer brake setup.

The only way I have ever seen a full 12VDC applied to the brakes to draw the 3AMPs per magnet is to pull the brake cable disconnect switch which will apply full 12VDC form your trailer battery directly to brake magnets...

I went round and round with my trailer brakes when I first got my 2010 Ford Truck. First I found out I had no 12VDC feeding my trailer 7-way connector which I finally figured out I was suppose to install a fuse and a relay which was inside my glove box in a plain unmarked zip lock bag. Once I installed this I had 12VDC feeding the trailer when I had my truck ignition key turned on...

Then I hooked up the trailer and went around the block a couple of times setting the OEM truck Brake Controller. This ended up being a 6 on the scale to keep the trailer brakes from from sliding going 30MPH.

The next problem I encountered was I did not seem to have trailer brakes engaged when stopped and holding down my truck brake pedal and I thought this was a real problem as having the trailer brakes locked up sitting at a stop seemed to be important to me. I did several home tests to insure my trailer brakes were working and eventually went to the Ford place with the problem. I was immediately told that the truck electronics has control of the OEM brake controller after 2009 with one being the brake controller disengages the trailer brakes when doing less than 10MPH when pushing down on the truck brake pedal. To override this they told to me use the manual slide brake if I felt like I needed to lock the trailer brakes down at a stop sign. Been doing that ever since...

About the only thing I did not measure was how much DC CURRENT was being used when the Brake PEDAL was pushed in or the manual lever was operated. I read the information about 3AMPS per brake magnet on-line somewhere on how to test your trailer brakes. Most likely from the etrailer.com site.

This was went I found out I needed a clamp-around cable DC CURRENT meter which I brought from AMAZON (Sears Model) and have used it many times measuring DC current associated with my battery banks but never thought to measure the cables when the brakes were being applied after I learned how they worked.

Now I can't find my portable AC/DC 400AMP Current tester anywhere. It is not where it is suppose to be and thats in my Truck Tool Box. I am thinking I left it sitting on a tree stump somewhere camping... geesch... (Another $60 loss haha)

Roy Ken

3.3^ seems way too high.