5th wheel brake issues

[RobertN]

My testing yesterday was done by plugging the 5th wheel pigtail in to the receptacle on the truck.

The trailer itself, is sitting in the driveway. Besides it's regular front stands/jacks and rear stabilizers, it is on jack stands with the wheels removed so I could pull the drums and inspect the brakes, and repack bearings.

So there is no mechanical connection thru the kingpin/hitch.

While grounding will occur through the mechanical trailer connection you cannot depend on that.

 

[RobertN]

My progress so far...

- I updated from my old Tekonsha Sentinel to a Prodigy P2.
- I have all 4 brakes functioning; the rear axle was not wired correctly.
- I found a ground at the front of the 5th wheel that needed cleaning/repair. It is more related to my deep cycle batteries than brakes...
- Previous owner put a 3' extension on the 5th wheel cable. And used butt splices. The ground was loose... Fixed that, but not much difference in voltages.
- I ohmed out from the 5th wheel plug to both the brakes and the ground. I have less than 1 ohm from plug ground pin to brakes grounds. I have less than an ohm from the plug to the battery /chassis ground. And, I have about an ohm from the brake pin on the plug to the brakes.
- With the Prodigy reading 12, I have 11.88V on the plug at the back of the unit. I have an in-bed 7-pin connector for the 5th wheel, and the original one at the receiver hitch. With the 5th wheel plugged in to the receiver hitch plug, I read 8.5V at the in bed connector, and 6.5V at the trailer brakes.
- Have not found a "junction box" where the 5th wheel pigtail feeds out to the rest of the trailer.

So at this point, I have a much nicer controller, some cleaned up ground and 4 brakes functioning, but still low voltage... And, it seems a lot of the voltage drop is in the truck.

 

[Ken45101]

- I ohmed out from the 5th wheel plug to both the brakes and the ground. I have less than 1 ohm from plug ground pin to brakes grounds. I have less than an ohm from the plug to the battery /chassis ground. And, I have about an ohm from the brake pin on the plug to the brakes.

One ohm at 12 amps is a 12 volt drop!!!

A half ohm here, another half ohm there....and your brakes CANNOT work properly

With high current and only 12 volts, you cannot have an ohm drop here and there.

Measuring resistance is a good start, but at this point I would run a long wire from your battery negative terminal to your voltmeter and start breaking down where your voltage drops are. Even a quarter ohm will give you a 3 volt drop.

Ken

 

[Deere Dude]

My progress so far...

- I updated from my old Tekonsha Sentinel to a Prodigy P2.
- I have all 4 brakes functioning; the rear axle was not wired correctly.
- I found a ground at the front of the 5th wheel that needed cleaning/repair. It is more related to my deep cycle batteries than brakes...
- Previous owner put a 3' extension on the 5th wheel cable. And used butt splices. The ground was loose... Fixed that, but not much difference in voltages.
- I ohmed out from the 5th wheel plug to both the brakes and the ground. I have less than 1 ohm from plug ground pin to brakes grounds. I have less than an ohm from the plug to the battery /chassis ground. And, I have about an ohm from the brake pin on the plug to the brakes.
- With the Prodigy reading 12, I have 11.88V on the plug at the back of the unit. I have an in-bed 7-pin connector for the 5th wheel, and the original one at the receiver hitch. With the 5th wheel plugged in to the receiver hitch plug, I read 8.5V at the in bed connector, and 6.5V at the trailer brakes.
- Have not found a "junction box" where the 5th wheel pigtail feeds out to the rest of the trailer.

So at this point, I have a much nicer controller, some cleaned up ground and 4 brakes functioning, but still low voltage... And, it seems a lot of the voltage drop is in the truck.

Did you try hooking up your pigtail to the plug in the rear if the truck instead of the one in the bed? It made a big difference in mine.

 

[Diamondpilot]

Yea, truck and trailer problems combined to give you weak brakes. Looks like you have lots of tracing to do.

Chris

 

[RobertN]

I did. Did not seem to have an effect. This morning I am going to try disconnecting the wire harness that goes to the bed, and connect the factory harness to stock. The in-bed connector was a "T" kit that has connectors on it, so it is easy to remove. I did check though, both receptacles were bright and clean.

Did you try hooking up your pigtail to the plug in the rear if the truck instead of the one in the bed? It made a big difference in mine.

 

[RobertN]

All this makes me wonder, how many folks out there have brakes that are not working right...

I have 24 years experience in electronics, most in a lab doing debug and failure analysis. Some, of actual memory chips and microprocessors(actually probing internal circuits on the chip with sub-micron probes in special fixtures), some fixing the equipment we used to test the chips.

But Automotive wiring? It drives me bonkers .

Yea, truck and trailer problems combined to give you weak brakes. Looks like you have lots of tracing to do.

Chris

 

[RobertN]

That was kind of the plan for today. My helper/in-cab brake activater is at school right now

Measuring resistance is a good start, but at this point I would run a long wire from your battery negative terminal to your voltmeter and start breaking down where your voltage drops are. Even a quarter ohm will give you a 3 volt drop.

Ken

 

[Diamondpilot]

Use a brick to hold the brake pedal down or you can use a bungee to hold the manual lever or even a clamp.

It sounds to me now that you have a major open in your trucks wiring. To save yourself a bunch of headaches I would get a buddies truck over to the house and test your trailer using it.


This may tell you what you already know but atleast it will verify what you know.

Chris

 

[RobertN]

I was thinking about that... I have a call out to see if one of my fellow Vol Firefighters can come over with his truck after work.

It sounds to me now that you have a major open in your trucks wiring. To save yourself a bunch of headaches I would get a buddies truck over to the house and test your trailer using it.