Trailer Brake Questions

I just bought a new Lawrimore 18' bumper hitch 7k equipment trailer with brakes on both axles and a break away kit. I wired in a Tekonsha P3 brake controller and 7 pin plug to my 85 Chevy 1/2 ton 4x4. Hooked it up to the trailer, and everything seemed to work. I took it to a large parking lot to set the brake voltage. I never could get the brakes to lock up even at max. 12 volts on the controller. But, it was applying some braking. I loaded up my little tractor and down the road I went, but when I hit the brakes, the controller would say overload when I really wanted to use the trailer brakes. It would say overload if I used the manual lever to apply max. voltage for braking also. If I applied them when coasting to a stop, it would apply .6 to 1.0 volts with the controller maximum voltage set to 6.0 volts. If I am sitting still, it will apply 1.3 or so volts after holding the pedal for a few seconds like it is suppose to.

Using the P3 diagnosis, it shows the battery volts = 14.??, brake volts = 14.??, trailer brake volts = 14.??, and trailer brake amps = 23.00. These were taken while sitting still.

All 4 brakes hum when brakes are applied. Another note: I wired the brake controller power wire and the trailer power wire to the same 20 amp circuit breaker on the aux. side. Then, I hooked the "bat" side of the breaker to the wire coming from the starter to a terminal mounted on the firewall that has constant 12v.

What seems to be my problem? Does the break away kit have anything to do with it. Yes, it is pushed in all the way. Bad ground on trailer?

My turn signals blink rapidly also. I have had this problem on any trailer that I hook to. How do I solve this also? I don't think the brakes and signals are related to each other's problems.

Ground can never be eliminated as a potential problem, but an overload indicates a short somewhere on the hot side of the brakes. I had a similar experience with my gooseneck.

In that case (it was still low miles, essentially new), a wire to one of the brakes chafed and was shorting to where it passes through the backing plate. Really aggravatin' to track down, as the controller didn't overload when stopped, and didn't overload when applied in reverse, only going forward. I was on the road and didn't have the gear I would have liked to have to track it down. Wound up snipping brake wires one at a time, one axle at a time, to nail it down. Fortunately it was on the first axle we snipped, so I still had brakes on the other axle to get home with.

I agree with Scotty, it sounds like a short somewhere. I"ve never checked the amperage draw on a set of brakes, but 23A sounds awful high. If you manually apply the brake controller without the trailer hooked up, it should read 0 amps. If it reads more than that, the short is on the truck.

As to your blinker problem, the cheap, easy, fast, but not right way, is to install a heavy duty flasher. The proper way would be to install a "powered taillight converter" such as a Valley #52280. I went through two of those on my pickup (I think I had Hoppy), then made my own with 3 standard 4 or 5 pin relays. This way, the turn signal and headlight switches are only activating the relays" coils. You"re not running the power for all your trailer lights through the truck switches, the trailer lights get their power direct from the battery.

Thanks for the advice. I think I found the problem last night. The brake wires running from right side to left side were connected together correctly, but they had another wire stuck in the same connector with a stripped end showing. These must have been factory testing wires that were never removed. They were touching the axles and leaf springs. I cut the ends off and taped them up and the problem has seemed to have gone away. That would answer the question of why it did not do it all the time.

I will try the heavy duty flasher idea first. That seems to be fast and easy.

Another question: The trailer plug does not use the 12V terminal, can I run a wire from this terminal to the positive on my breakaway battery? Will it overcharge it? What is the 12V terminal normally used for?

Glad you found the short. Hard telling what that wire was for, but as long as you wound up with four good brakes, it doesn't really matter.

The 12v pin has different uses. On the truck side, it is usually wired in to be hot all the time, regardless of the position of the ignition switch. On box trailers it provides the juice for interior lights, and used similarly for auxiliary lighting on open beds. If you put it to that kind of use, you'll need a separate switch for the aux lights on the trailer. Without one, you'll have the lights on all the time going down the road, and you can run your truck battery flat if you leave them on while parked for too long with the engine shut down.

They do sell a small charger for breakaway batteries that can fit in the box with the battery if there's room or, if not, bolted to the frame nearby. Those chargers draw their juice from the 12v hot you're talking about. (Look around, including in the battery box, to see if you already have one, though I tend to doubt it if they don't have the aux-pin hooked up.)

You need to be careful hooking that 12v up to the breakaway (other than through the charger, which should be self-regulating, and typically limit the charging amperage to 1.5 or 2 volts) or any other battery (say a battery that you want to keep charged for running a winch, or camper storage batteries). The possibility you mentioned of overcharging is one issue.

Another (more important with bigger, trailer-mounted batteries like for a winch) is isolating that battery from your truck's battery. You can burn up an alternator and ruin your truck's battery(ies) trying to charge a full-size battery on the trailer that has gone bad. Try etrailers.com. They have the isolators, I believe, as well as good reference sections explaining better than my feeble effort as to what they do and why you might want one.

First off, a fix to the post below where I said the breakaway charger limits the charging amperage to 1.5 to 2 volts. Not sure what I was thinking. That obviously should be 1.5 to 2 AMPS.

Now, as to these stray wires . . . Are you sure you have four brakes? I ask only because it sounds like you had one on each axle. It's not inconceivable that the two wires were intended to be joined together to make the jumper to carry brake voltage to the rear axle. Most trailers run the brake wire from the plug down the left side to the left front wheel. From there, the wire should branch off in three directions -- one into the left front brake, another across to the right front brake, and the third to carry voltage to the right rear brake, where it will branch off just once more across the axle to the right rear.

It wouldn't be hard to imagine a builder of a tandem putting a lead out of the left wheel of each axle so that all they had to do to run voltage to the rear axle was splice the ends of the two leads together. Was it the "spare wire" on the front axle that was contacting the springs? If so, it'd be worth checking out closely to make sure you've got a connection to the brakes on the rear axle.

Here is how it was wired.

Power and ground wire "together in insulation" goes to the right front brake. Then branches in 3 directions (one set to right front brake magnet, one set through axle tube to left front brake, then third set is the jumper to the right rear brake. Then, the right rear wires are connected to its magnet wires and from there another set through the axle tube to the left rear. I think we are saying the same thing except mine starts on the right side.

So, picture this. On the left front brake there are 3 sets of wires. One is the main lead from the right front brake, one is the actual magnet wires on left front brake, and one set just stubbed out about 6 inches with ends stripped off. All 3 sets + and - are connected using wire twist connectors. The left rear brake is the same way except it receives its feed from the right rear brake.

Are you confused now?

It seems the short stripped wires would be used for factory testing to make sure the + and - were hooked up correctly after being stuffed inside the axle tube from the right side to the left side. They used the same color "red" for both + and - brake wires.

All 4 brakes do work (humm). I checked each one while someone pushed the manual lever on the brake controller. I haven't driven it except up and down my 500' driveway, but I can stop instantly and feel the trailer brakes jerk the truck when I really crank up the voltage setting and also lock up the trailer wheels (not sure how many) and make them slide on the gravel.

Yep, same setup except with the main lead running down the right instead of the left as I described.

Those stray wiress are a little weird, never encountered such a thing, but if they're out of the picture now and things are working as they should, it sounds like you're good to go.

Happy motoring!

When i towed my travel trailer for the first time, i had a grounding problem in the wiring. So, i made a separate ground wire from the trailer frame to the car frame, with a plug that could be pulled apart when unhitching, and put back together when hitching up.

The guy I got my controller from says that one company makes all four(?) major brands, they just put different stickers on them.

When I wired my trailer, I ran power down both sides then connected them across the back axle.

The magnets must not be polarity-sensitive? I hooked a weak battery both ways to a brake and tried moving the trailer, and it grabbed both times. Both magnet wires were green and I don't have any errors on my controller so I guess either they aren't or I got lucky?