2005 Ram 3500 QC, Prodigy P3 brake controller (plug n play to truck harness) 2013 Jayco White Hawk 27DSRL (Dexter Axles/Electric Brakes)Recently did a quick weekend to St. Augustine. Hooked up trailer doing brake check and manually activate trailer brakes, brake controller says trailer not connected. Checked 7 pin connector, went under trailer checked brake wiring no problems seen. Two 30 amp fuses at trailer positive cable battery connection, checked them, no problem (what are those fuses for anyway? They are on wiring between battery and a junction box of trailer frame, the tongue jack is separately fused). 90 minute trip up the road, flat terrain, good weather, truck brakes have plenty of whoa for truck and trailer so off we went. Got to campground and checked the truck's fuse for the trailer brake cicuit, it was blown. Replaced the fuse, hooked up the this morning and all is good. Brake check, manually activate the trailer brakes, no problem. Had the voltage output on the controller set to 8 volts. Brakes worked fine, typically drawing 5.9 volts when I hit the whoa pedal. Get off I-95 to head home apply the brakes and controller once again says trailer not connected. Haven't checked the fuse on the truck yet, but pretty sure I'm going to find it's blown.I hope I provided enough info for the mechanical sleuths out there, but I'm at a loss for where to begin. In 3 years, I've had zero issues with the trailer brakes, and am inclined to think the problem is with the @#$%^& truck. The only thing I did to the trailer brakes prior to leaving was adjust them. Any thoughts, suggestions, quick cures? Thanks.

Sometimes the plug will work OUT a little, and break connection

Not the problem. Especially when we started out on the trip, I didn't go 40 feet in the storage facility. I didn't check the truck's fuses til we got to the campground. I've had the truck 7 years, have towed a fifth wheel with electro- hydraulic brakes, now this travel trailer with electric brakes and the entire time with the P3 controller, and never a problem......til now.

Because you are blowing a fuse, that comes from an overload condition. The most likely cause of an overload is a loose connection somewhere. It could be the positive feed, or equally as likely, the negative return. It might be in one particular wheel, or it might be in the main feed. I would definitely start with both sides of the plug in connector first. The trailer brake fuse feeds out to the brake coils, and comes back on the common return with all the other neutrals. The neutral wire carries the heaviest load always, so a loose neutral is the most common problem, not the positive feed. As the connection becomes loose, it heats up, and then causes corrosion and then you have a higher load than the circuit is supposed to handle, and the fuse blows.

Boy I'd really do some diggin into the trailer wiring. I don't like hooking up to a new trailer before I check the plugs. Your TIPM on the truck is expensive and it sounds like it reset in the middle of your trip. To many resets and it will just flat out fail and need to be replaced. That is one thing I hate on Ram trucks. Hope it is something easier though like the prongs needing to be spit more for contact. Could also be a short in the trailer wiring in the axle area. Shafting in the axle tubes is a common problem. Good Luck

Thanks 'bird. This is gonna be a daunting task, there's a lot of wiring to check. Not related to the brake issue, but our last trip out the 10 amp fuse on the truck that protects the circuit feeding the clearance lamps on the trailer blew. Replaced that and no problem since. This truck has developed a history of electrical gremlins, this brake issue is just the latest. May well be the trailer brakes but the truck's recent history isn't helping.........

Trailer Brake or Truck Problem? | Good Sam Community

31 Replies

BenK
Explorer
Jun 20, 2015
You have an intermittent short/open...toughest thing to find on electrical
systems...
thomasmnile
Explorer
Jun 20, 2015
The plot thickens........Last night drove about 9 miles to a local restaurant in a thunderstorm (not especially heavy rainfall by Florida standards) and I suddenly notice the display on the P3 controller flashing a message stating 'Warning' Short to Battery No Brakes! In 8 years I have NEVER seen that message, with or without the trailer connected. All good info. but the trailer wasn't within 15 miles of the truck, let alone connected to the truck. Checked the electric trailer brake circuit in the truck fuse panel (the previously blown 30 amp)and it was fine. Matter of fact, when I reinserted the fuse then checked the brake controller, it had reset itself from the warning message and was displaying the normal home screen shown when the truck's ignition is on.

What in Gawd's name is going on? Inclined to take the truck to my mechanic, but would really like to have some idea of how to explain this weirdness so they aren't flying completely blind attempting to diagnose what may be happening.
kaydeejay
Explorer
Jun 05, 2015
gkainz wrote:
CampingN.C. wrote:
Can't argue with the ol' Ohms Law !

Well... you can ... but resistance is futile. :)
Oh my, that is shocking!!!
gkainz
Explorer
Jun 04, 2015
CampingN.C. wrote:
Can't argue with the ol' Ohms Law !

Well... you can ... but resistance is futile. :)
CampingN_C_
Explorer
Jun 04, 2015
kaydeejay wrote:
Perrysburg Dodgeboy wrote:
Just a question for the electricians here. If a lose connection creates heat and it does would it not also increase the amps needed to power the circuit? Almost every campsite electrical box is worn out and some are so bad that it will even melt the cord. The ones like this all would trip the breaker. Heat is a sign of heavy draw right?

Don
Heat is the result of a high resistance connection, not an increase in current flow. In fact the reverse is true, current may be limited by that high resistance connection. A voltage drop across the connection will ALWAYS create heat, the amount will be a function of the current flow.

Many campsite receptacles are worn to the point that they make poor contact with the plug, aka high resistance, hence heat, resulting in melting the plug.
For example, if there was a 10 volt drop across the connection, drawing a 30amp current, then 300 watts of heat is going into that plug. I think you can imagine the result!!

Can't argue with the ol' Ohms Law !
Perrysburg_Dodg
Explorer
Jun 03, 2015
kaydeejay wrote:
When did the 110volt side if your system come up??
Everything we have been talking about re your truck and trailer, especially brakes, is 12 volts.
I still say you have a chafed wire that is creating an intermittent short in your brake circuit.

The 110V was never an issue, I had made a comment about heat and used the campground power supply overheating my plug and tripping the circuit breakers.

The OP does not have a AC electrical problem. Sorry if my analogy confused anyone.
BenK
Explorer
Jun 03, 2015
Careful...

Modern vehicles and their computers can be FRIED by some testers....especially those with a 9 volt battery inside it

Some Signal level voltage can be less than one volt...or be current sensing (milliamp)

Ben
Via smartphone phone...excuse my fat finger typos
kaydeejay
Explorer
Jun 03, 2015
thomasmnile wrote:
kaydeejay wrote:
When did the 110volt side if your system come up??
Everything we have been talking about re your truck and trailer
Um, not quite. Go back 1 page. Since I had the truck in for the Takata recall, service writer asked if there was anything else. Told him about the trailer brake issue, and could they check the truck wiring and replace the fuse. They had the truck two days, wasn't done.

Once bitten, twice shy with this dealership. Took it there to run down a problem with the electrical system last September, dash volt meter was showing less than 12 volt output. Had it all day, scanned it they said could find nothing wrong and collected $105 for their 'effort'. Problem persisted, took it to the mechanic in Orlando that regularly services the truck, they found a problem with the cooling fan clutch and replaced it. No voltage output problem since,normal 14.2 v output. Don't pretend to understand that, but I do know the cooling fan now works, I'm not certain it ever has in the last couple of years.
What does any of this have to do with 110 volts?
thomasmnile
Explorer
Jun 03, 2015
kaydeejay wrote:
When did the 110volt side if your system come up??
Everything we have been talking about re your truck and trailer

Um, not quite. Go back 1 page. Since I had the truck in for the Takata recall, service writer asked if there was anything else. Told him about the trailer brake issue, and could they check the truck wiring and replace the fuse. They had the truck two days, wasn't done.

Once bitten, twice shy with this dealership. Took it there to run down a problem with the electrical system last September, dash volt meter was showing less than 12 volt output. Had it all day, scanned it they said could find nothing wrong and collected $105 for their 'effort'. Problem persisted, took it to the mechanic in Orlando that regularly services the truck, they found a problem with the cooling fan clutch and replaced it. No voltage output problem since,normal 14.2 v output. Don't pretend to understand that, but I do know the cooling fan now works, I'm not certain it ever has in the last couple of years.
kaydeejay
Explorer
Jun 03, 2015
thomasmnile wrote:
Well, my issue isn't with the 110v power, but I bought a good test light today and will begin the detective work starting with the truck, which I just got back from the dealer for the Takata 'airbags of death' recall repair. Both driver and passenger bags replaced.
When did the 110volt side if your system come up??
Everything we have been talking about re your truck and trailer, especially brakes, is 12 volts.
I still say you have a chafed wire that is creating an intermittent short in your brake circuit.

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Trailer Brake or Truck Problem?

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