remove trim to replace breakaway switch

[Dave27]

The break away apply bypasses the truck apply and connects the trailer battery 12V to the trailer brakes (blue wire). One wire to the break away switch should be trailer battery 12V. The other wire will be a “ground” through the brake electro magnets, so will have some resistance if measured to chassis ground with an ohm meter.

Rob

Cate&Rob Country Campers
Rob - I don't understand your comment about "ground through the brake electro magnets." The replacement switch I bought has three wires. Two will replace the existing two, and one is grounded to the frame. From what Brian says, splicing into the two existing wires makes the most sense.
thanks, Dave

[Cate&Rob]

Dave27


Three wires on a break-away switch . . . hmmm. I have only seen two wire versions. I don't understand why this 12V switch would need a ground connection.
Make sure that third wire on the switch does not electrically connect to either of the other two wires with the pin either inserted or pulled.

The wire from this switch that is going to the blue wire in the junction box and on the the brakes will "see" the resistance of the four electromagnets that apply the brakes when compared to a chassis ground.

Nothing wrong with splicing into the two existing wires . . . if the problem is in the switch and not in the wiring.

Rob

[Dave27]

Dave27


Three wires on a break-away switch . . . hmmm. I have only seen two wire versions. I don't understand why this 12V switch would need a ground connection.
Make sure that third wire on the switch does not electrically connect to either of the other two wires with the pin either inserted or pulled.

The wire from this switch that is going to the blue wire in the junction box and on the the brakes will "see" the resistance of the four electromagnets that apply the brakes when compared to a chassis ground.

Nothing wrong with splicing into the two existing wires . . . if the problem is in the switch and not in the wiring.

Rob

Cate&Rob Country Campers I don't know for sure if the old switch was working or not, the new one is (it has an LED on when it's activated), and the brakes aren't activated when the switch is. So there is probably a brake wire issue. How do I trace the brake wire?
thanks, Dave

[howson]

Dave27
Is the new breakaway switch similar to the Hopkins switch on etrailer's website? https://www.etrailer.com/p-HM20059.html

If it is, I'm confident the white wire is a ground for the LED only. The breakaway is literally just an on/off switch. https://www.etrailer.com/question-21465.html


The way my 315RLTS was wired, there were two black wires coming out of the OEM-supplied switch. It's just a switch--there's no polarity. One wire went to an always-on connection at a self-resetting circuit breaker and the other (as described in previous posts) was wired directly to the blue wire in the trailer's junction box.

One more thing--and I apologize if I missed it above, but have you confirmed the brakes work with the tow vehicle connected?

[Cate&Rob]

Dave27
Hi Dave,

The LED on the switch would explain the need for the ground wire.

Do the trailer brakes work correctly when connected to the truck? If so, the problem is between the break-away switch and the connection in the trailer junction box. The output of the break-away switch should provide 12V to the blue wire in the junction box. If the trailer brakes do not work when applied by the truck circuit . . . the problem is further down stream. Power to the trailer brakes goes first to the left front wheel. Then across the axle tube to the right front wheel and back to the rear axle. These wires will be accessible where they drop down from the underbelly to the axles.

I would start by checking for 12V at the wire drop to the left front axle, with the break-away switch pulled.

Rob

[Dave27]

howson Cate&Rob
Yes, it is exactly like the Hopkins switch. The brakes work from the truck. Thank you for the explanations of how the system works. I know what to check next.
Dave

[Jlawles2]

Dave27 Dave, if the led is on when the switch or brakes are not activated, you need to reverse the in and out leads on the switch. The LED on the switch should be downstream (non power side) of the switch otherwise it has power at all times. I would not think they went through the trouble of installing a separate micro switch in the housing just to turn on the LED.

[Yoda]

howson Cate&Rob
Yes, it is exactly like the Hopkins switch. The brakes work from the truck. Thank you for the explanations of how the system works. I know what to check next.
Dave

Dave In post #4 you show the junction box, Below the blue wire going to the trailer is another wire - it appear to be black - where does this wire go?
Trying to help.
Keith

[Dave27]

Dave27 Dave, if the led is on when the switch or brakes are not activated, you need to reverse the in and out leads on the switch. The LED on the switch should be downstream (non power side) of the switch otherwise it has power at all times. I would not think they went through the trouble of installing a separate micro switch in the housing just to turn on the LED.

The wires are clearly marked on the new switch, one to battery, brakes, and frame ground. I checked which one was hot before I disconnected the original switch. It worked fine.
thanks, Dave

[Dave27]

Dave In post #4 you show the junction box, Below the blue wire going to the trailer is another wire - it appear to be black - where does this wire go?
Trying to help.
Keith

The black wire came from the switch. Both wires are black on the original switch, one ties into the battery somewhere, and one links to the blue wire. When the switch is pulled the brakes are powered on.
Dave

[Yoda]

The black wire came from the switch. Both wires are black on the original switch, one ties into the battery somewhere, and one links to the blue wire. When the switch is pulled the brakes are powered on.
Dave

So is everything working now? BTW the one that ties to the battery is the black wire I mentioned tying into the buss bar in the front bay.

[Dave27]

So is everything working now? BTW the one that ties to the battery is the black wire I mentioned tying into the buss bar in the front bay.

The new switch works and checking after the fact, so did the original one. I tested continuity at the junction box. I separated the black wire from the switch from the blue one to the brakes. The switch had continuity when the breakaway was pulled, and not when it wasn't. I also have continuity on the brake wire, but the brakes don't activate when I power up the system and pull the breakaway. I am puzzled by this. When I get a break in the weather, I will take the next step Rob suggested, check for power at the first drop of the brake wire at the right front wheel.
Dave

[Jlawles2]

Dave27 Dave, you may have none to 4 of the brakes working. It's not an uncommon thing to find that the wiring connection at the axles is not doing it's job based on what I've seen here and in both of my other campers. I've seen professionally installed components where they "FORGOT TO REMOVE THE INSULATION" when making a butt spice. So do not be surprised if you find bad connections at both axles.

[Dave27]

Cate&Rob Hi Rob,
I have power at the the first drop at the front axle. I measured 10.8v from the hot wire to the frame. I recombined the three wires on the hot side, and did the same with the three ground wire in a way that I could take the voltage across them. There is no "buzz" in the brake when I pull the breakaway switch. I measure about 9v between the combined wires. Power is being drawn, I noticed the battery voltage dropped. Could there be something wrong with the brake itself? I heard the brake buzz when it was hooked to the truck when I stored it. Could the higher voltage coming from the truck's alternator make a difference?
Thanks, Dave

[Cate&Rob]

Dave27
Hi Dave,

Drum brake electro magnets don't usually make any noise when they are powered up. The brake apply "gain" adjusts the supply voltage to adjust the power of the electro magnet that is dragging on the spinning brake drum to apply the brake shoes. An indication as to whether a brake is getting power is to place a magnetic compass near the lower part of the brake drum where the electro magnet is located. As the brakes are energized, the compass needle should swing in response to the magnetic field. This does not give you a measure of how effective the braking action is . . . just that the magnet is getting power.

The break away switch should apply full trailer battery voltage to the brake system. Measuring 9V at the brakes from a (presumably) 12V+ at the battery indicates some significant resistance in the wiring.
Each electro magnet should draw 3A at 12V. Even 12A for all four brakes should not be enough current to measurably draw down a well charged battery if the wiring is in good shape.

Rob