My trailer brake voltage has dropped, suddenly. Have weak brakes. Here is the scoop.
Brakes working just fine, then all at once, gone weak. Factory wiring in truck. Reese Brakeman Compact controller. Voltage at truck rear bumper plug, 12.5V,
Voltage at end of truck to trailer harness, 9.85V. Voltage at first t-off to trailer brake, 5.45V. Does this sound like ground problem, or defective controller, or what. I have spent six hours under trailer inspecting/redoing connections, but no improvement. Must have brakes, as this is 46ft trailer, that travels 4 days a week. I have run out of things to check. I don't want to start just throwing parts at it, but do not know what to do at this point. Anybody got any ideas what problem might be.

 

I like to start with the simple[and cheap] stuff 1st just general to electrical problums , if you get no function to a deivice then its comin that theres no power [ and we all want more power] if you have some function then its a partial ground [ maybe just a few strands left in the wire or ground found a nother path-not good for computor controled ] so your leaning towards the ground would be my first choise , try a long wire from battery neg. to neg. at wheel , that should be a positive test . then check with meter every few feet back to battery till you find a voltage drop or high resistance .

 

I think I am confused. You say you have 12.5v at "truck rear bumper plug". Then you say "Voltage at end of truck to trailer harness, 9.85V". What is the difference in those 'two' (???) points, or are they not the same point?

With the controller set at max, if you have good voltage at the plug, check ground first, then the advice to work down the line and check the voltage drop across every connection is right on. The wiring is normally in series, meaning each magnet gets a part of that voltage. Look for the one that is dropping the most - - there is your high resistance point.

Bob

 

Is this an intermittent problem or is your voltage always low? Does you're wiring go inside your axles? I have had several trailers that the wiring chaffed inside the axles until they grounded out. I ended up running the wires extenally. Hope this helps.

 

As suggested earlier, pull a ground wire from the truck battery. Then start checking voltage from anything positive on the trailer to the temp ground. In 12v vehicle systems, the problem is almost always the return or ground. I had a bad ground on on of my trailers and when I turned on the lights I saw the back up lights on. Eventually it blew the fuse to the back up lights.

 

FiverBob. No, not the same point. First point is inside plug on rear bumper, measuring voltage pin to pin(blue brake wire to white ground. Second point is at trailer where cable from truck to trailer, is wired into 4in square box.(measure voltage blue wire to white wire. This is first drop(12.5v to 9.85V). Next measurment is under trailer where first brake t's off from mail trailer wiring to brake(5.45V). From there each brake measures apx same voltage(5.45v). Dexter says these brakes should be wired parallel(these are). Have checked or redone all connections, but no improvement. If controller is bad, I should not get 12.5V in bumper blug, right? Continuity in wiring harness(truck to trailer checks OK, blue and white wire show 0.00 resistance. Also Dexter says brake ground should be commmon(this is the case). Also, some trailer sites, on internet, say that regular volt meter will not show true voltage on electric brakes. I don't know about this, but am ready to pull out somebody's hair, or resort to high explosives. I don't mind replacing parts, but I need to identify what is bad. This problem is constant. Also if I apply voltage, for extended time(min 1 min), trailer wires start to heat up to touch.

I think I have answered all questions. If not, please ask again. I got to get this fixed, and get back on the road.

Thanks for all help.

 

Trip,
When you check the voltage at the trailer junction box I bet the brakes are activated. This would cause a voltage drop. I suffered the same type problem with a brand new horse trailer. The closer I got to the brakes the less the voltage due to the wire size. Dexter recomendes a BIG wire for no voltage loss! All the new trailers I have bought don't pay attention to that recomendation! But they still seem to work OK?! Anyway if you diconect the brakes the I bet you have your 12v at the brakes (I have been wrong lol). I even suspect my truck wire size. I have two trailers that seem to have less stop with my 3rd gen over my old 2nd gen (anybody else?) ....oh yea you mentioned hot wire...to small of wire will do that! Or if the brakes are out of adjustment you have to throw more volts to get them to kinda work the longer they are on will cause the wire to heat up.

 

How many miles on the brake puck [ the magnet that touches the drum ] if you hot wire the brakes and the wire heats up , It may be a clue that maybe the puck is warn down to the windings and shorting out , just a nother thing to look at .

 

John,
My new trailer had the same voltage drop the closer I got to the brakes. It ended up being the trailer Mfg. got a lot of Magnetic pucks from a new supplier and they were putting a rust prevenitive coating on them....bad idea! need I say more....I bet Trip's problem is at the brakes...adjustment or puck?! other...Maybe?! I been there it will drive you nuts! You can check the resistance at the puck and that will tell you if there is a problem.

 

How old is the trailer connector at the bumper? Look at the contacts...Are they oxidized? If so, you may need to change the plug. The oxidation is a high resistance path. I had that failure this last spring, but on the Left brake light.

HTH

Tony

 

I agree with Tony B. A good place to start is with the bumper plug. More often than not the problem is there. Moisture gets into the back and over time corrodes the terminals inside. Take it apart and check it. Install new or clean it up and pack with dielectric grease to prevent future corrosion. Once you have that done, start checking any connection that exists from the trailer plug back, paying special attention to grounds. Good luck

Casey

 

Thanks everyone. Tomorrow, if not raining, will start to check on these new things. One thing, the trailer brakes are wired with 14 or 16ga wire. This is too small is't it? The trailer connector I have(7wire)is 6/16ga, 1/14ga(white ground). Do you think it cannot carry enough juice for six trailer brakes? I have one brank new backing plate, and five originals. Voltage checks almost the same, but will try to test resistance tomorrow.

I noticed on internet, Reese Brakeman Compact is only recommended for 2 to 4 brakes. Is it possible, controller will put out enough voltage, but not enough amps for six brakes?

 

Yep....amps are real important! Six magnnets draw a lot more than 4! ..Did the brakes used to work or is this a new aquired trailer?

 

Brakes worked for a while. I discovered one dead magnet. Replaced entire backing plate, with identical unit from Dexter. That's when my problems started. If controller is bad, why would I get 12.5V at truck bumper plug? If brakes are wired in parallel, how would one brake pull voltage down so much? I have one dead magnet now, one brand new one, and four originals. I think I am going to go ahead and get a new controller, but I am not confident this will solve the problem.

 

Brakes are normally wired in series. That is why it is so important to have good connections all the way down the line. You might want to put an ammeter in line and check the current drain. If you have a Jordan controller, it shows the current being drawn, not voltage. It should be around 2-1/2 to 3 amps per magnet.
Bob