Airstream Forums

Airstream Forums (
-   Electrical - Systems, Generators, Batteries & Solar (
-   -   Brake fuse (

Over59 02-07-2005 08:28 AM

Brake fuse
Does one fuse the brakes. The wiring diagrams don't show fusing for any of the trailer running lights, ect. While some of these curcuits may fuse in the TW it looks like the brake line comes unfused off the tw control panel aux post to the Brake controller then on to the brakes. Should a fuse be in there somewhere to protect the brake controller. I was thinking an inline fuse at the connector box in the trailer for each axel.

Inland RV Center, In 02-07-2005 08:48 AM

Protecting an electrical brake line with a fuse or circuit breaker is taboo.

The idea is to have some kind of brakes, even though a short or partial short developed.

Partial shorts usually come from worn out brake magnets.


Over59 02-07-2005 09:01 AM

Thanks Andy. Kind of thought that may be the case. Better to have brakes with smokin wire than good wire and no brakes.

markdoane 02-07-2005 09:45 AM

Isn't there supposed to be a fuse or circuit breaker in front of the brake controller?

Inland RV Center, In 02-07-2005 10:14 AM


Absoluely not.

The theory is that even with most shorts, you will still have some braking.

It is far better to be able to stop, than to be worried about some smoking wires.

The short can be fixed. Your life cannot.


markdoane 02-07-2005 10:57 AM

I'm just repeating what I see in the installation instructions for brake controllers. Most specify a 20a circuit breaker.

I don't follow your logic about being able to stop, rather than worry about smoking wires. If the brake circuit is grounded enough to trip a 20 amp breaker, then there's probably nothing getting through to the magnets anyway. And if you have a short on one side only, feeding full amps to the other side could cause the trailer to trip sideways.

I think you should have a fuse or breaker in front of the breakaway switch too.

Just my personal opinion, not a theory.

Safari Tim 02-07-2005 11:11 AM

I agree Don, a fuse or circuit breaker is needed. At least you won't be on FIRE when you can't stop ;-)

To clarify, the circuit breaker/fuse is in the tow vehicle on the wire that feeds the brake controller. And all fusing is done right next to the battery positive post, as close as possible.

There is no fuse for the brakes on the trailer itself.

87MH 02-07-2005 12:13 PM

Breakaway Switch Fuse/Breaker

Originally Posted by markdoane
.....I think you should have a fuse or breaker in front of the breakaway switch too.....

Having become quite intimate with the electric panel on the '78 Sovereign, I know for a fact that there is a 50 amp breaker on the line feeding the breakaway switch (this line is common to the electric tongue jack). The feed line from the breaker to the front (jack/breakaway switch) is only 12 gauge wire.....

The phrase "too hot to handle" comes to mind, quickly followed by "lit up like a Christmas tree".

I agree with Inland Andy - on the breakaway - since you have no way to monitor the trailer (breakaway) system, it would be unwise to install a fuse on the breakaway system.

Inland RV Center, In 02-07-2005 12:15 PM

Dealing with theories, opinions, guesses, or logic, is not the same as factual proof.

First of all, a fire will not start if you have a magnet shorted.

Secondly, controller manufacturers, because of liability, suggest fusing.

Third, all of us have choices to make.

If you wish to have no brakes, because you had a short, just to save some wiring, that's your choice.

Most owners, want the security of knowing that even with a short, they will still have some brakes.

Lastly, since power will not be applied to the brakes for more than a few seconds, that is not enough time to overheat the wires.

Also, the wires themselves offer some resistance in addition to the magnets resistance. Therefore, it is impossible to get a "dead" short.

That being the case, the heavy wires will get hot, but they won't burn.

Bottom line is how well someone choses to be as safe as they can, regardless of the circumstances.

Ask any pilot.


markdoane 02-07-2005 12:31 PM

I would certainly encourage anybody to think very carefully about the advice given in the above posting by Inland RV. If you don't have enough experience to figure it out, ask someone you trust.

I ain't no fool. I'm going with what feels right, which means every wire should have circuit protection. That means a resettable breaker ahead of the brake controller, and a fusible link or breaker on the breakaway switch.

Inland RV Center, In 02-07-2005 12:52 PM

There is a marked difference between somones opinion, and 39 years of dealing with any specific problem.

That becomes factas well as experience, our ageless teacher.

Anyone, I am sure, that had to stop quickly, would readily agree that to have some brakes, gives them a chance.

To have no brakes, gives a person, a big fat zero chance.

Don, the choice is yours, as well as theirs.

Leading anyone down a road with zero brakes, is not my idea of safety.

But, again, that's your choice. My only advice would be don't lose your brakes, and hit someone, or, get into a sway, and find out you have zero brakes.

That's not a good situation for anyone to get into.

Stopping a trailer, at all costs, when necessary, is the object. What it may cost to do that, very quickly, becomes insignificant, under the circunstances.

Safety, when dealing with lives, has no cost.

I have been there and done that, personally, with test trailers, single as well as tandem axles.

But the real bottom line, is convert to disc brakes, and then the fuse question becomes meaningless.


markdoane 02-07-2005 02:26 PM

So once again, 39 years experience means that you have all the answers, and everyone else is wrong.

Happy for ya.

Safari Tim 02-07-2005 02:31 PM


Originally Posted by Inland RV Center, In

But the real bottom line, is convert to disc brakes, and then the fuse question becomes meaningless.



Like they always say, 'Follow the money'.

Most tow vehicles come prewired today with a brake controller pigtail and fuse in the glove box to be installed by the brake contoller installer. There is a fused brake controller feed built into the tow vehcile fuse box.

The AS, even my '71 has 40 amp fuse which leaves the battery location to the tow vehicle where it is tapped off there to the electric jack and break away switch.

Power should always be fused or breakered at the battery positive post. And if two batteries are connected together as in a trailer/tow vehicle, they need to be fused at both ends.

One more note. The short may not occur in the brake itself, it may occur anywhere along the length of wire and with no fuse protection you have a very real chance of a fire starting.

TomW 02-07-2005 02:42 PM


Originally Posted by Inland RV Center, In
...But the real bottom line, is convert to disc brakes, and then the fuse question becomes meaningless.

The hydraulic pump (aka a possible failure point with disk brakes which drum brakes do not have) will need a healthy chunk of power to do its job.

Following the "don't put a fuse on the controller" argument, it would appear that the pump falls into the same frame of reasoning.


87MH 02-07-2005 02:49 PM

Breakaway Circuit Protection and Test

Originally Posted by TomW
Following the "don't put a fuse on the controller" argument, it would appear that the pump falls into the same frame of reasoning...

I think I have have been enlightened to the wisdom of the Airstream way of doing things.....

Yes, the breakaway circuit is on a very heavy breaker, and yes, the magnets will fail if a short circuit should occur,


the circuit is tested each and every time you hook the tow vehicle to the trailer....with the operation of the electric jack!

Power to the jack means power to the breakaway switch!

A failproof circuit test each and every time you hook up.


TomW 02-07-2005 02:52 PM

I put a 30 amp self-reseting breaker on the input power lead to my Prodigy controller because Tekonsha recommended it AND because I reasoned that the only thing that would trip it would be a dead short.

If a dead short is present, no power will make it to your brakes because it will all go to the short.

A fuse would not be a good idea because once it goes, its gone. With a self-reseting breaker, you get multiple chances to see if the short is intermittent.


Ga Pockets 02-07-2005 02:54 PM

The auto reset circuit breaker( 20 or 30 amp depending on # of axles) is between your Tow Vehicle's 12 volt system and the controller. If your charging system were to have a voltage spike or over current draw your system, your controller is still intact and will be workable in a few seconds after breaker cools and resets. If your controller gets fried..........a fuse down stream is a non-issue as you won't have brakes.

Wiring Instructions For Electronic Brake Controls

3. Connect BLACK (+) wire through an

automatic reset circuit breaker (20 amp for
1-2 axles, 30 amp for 3-4 axles) to the

POSITIVE (+) terminal of the battery.

The BLACK wire is the power supply

line to the brake control.

The BLUE (brake output) wire must be

connected to the trailer connector’s brake wire. (no fuse)

Inland RV Center, In 02-07-2005 03:11 PM


No, I do not have all the answers.

But I do have the background of seeing almost any type of Airstream problem that someone can dream up.

What I try to report, is that experience factor, of what and why, and the fix.

The choice is still up to the individual owner.

All coins have two sides. Some are OK, some are less than OK. Each individual makes their own choices, of describing safety.

Safety issues are far removed from liability issues.

The only arguement is in the case of a brake line short, almost always caused by a worn out magnet, is it safer to have some brakes, or no brakes?

My 39 years with customers and insureds, say they would rather have the former, namely some brakes.


john hd 02-07-2005 04:37 PM

not to jump in here and stir things up.

however, with your average battery in a tow vehicle being able to produce 650 amps, most wiring will become the fuse itself.

all in all, i'm with andy on this one. even though my rig is fused from the factory. 60 amp fuse, it will destroy the wires before blowing.

i think a good comprimise is a self resetting circuit breaker.


Over59 02-07-2005 09:33 PM

Well I guess I asked a good question. There is a resetting breaker between the controller and the power when I looked more carefully. Installed by the dealer with the controller. So if the controller lights are on I have juice going aft. I'll be running separate lines to the axles from the connection block, one for each axle. I'll fuse the hitch jack inline. I will not fuse the breakaway switch and don't see any reason to do so. I wouldn't want a damaged fuse / breaker to go unnoticed and then not have power available to the switch if needed. Using the same line as the jack would help but I've blown that line fuse with a bad switch and had to use the hand crank when I ran out of fuses. I guess I would have the same concerns about fusing brakes aft of the controller, wouldn't know if they were bad. I'm not sure I would notice the difference between one and two axles braking until I really needed them both. Seems like something could be built into the controller to indicate there is a short on the system. This part of the technology has a long way to go. You would think that the new units would have something different than my 59.
I have another question but I think I'll save it.
PS. Still obsessing over the Duramax and 8.1L. If only diesel wasn't more than premium gas.

All times are GMT -6. The time now is 05:41 PM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.