Truck not charging RV batteries

[DougKirby]

The two batteries in my 2008 Big Horn RV do not appear to be being charged by the truck but are being charged on shore power, here is some data, please advise recommended checks and remedies, thank you.

Truck disconnected from RV, RV connected to AC shore power.
13.2 Volts at both RV batteries

RV not connected to truck or AC shore power.
RV battery on right side 12.62 volts
RV battery in front compartment 12.61 volts

Truck at idle, RV connected to truck not connected to AC shore power.
Left drivers side battery in truck 13.80 volts
Right side truck battery 13.79 volts
Voltage at truck output in bed 13.78 volts
RV battery on right side 12.71 volts
RV battery in front compartment 12.71 volts

I think this is the key point, 12.71 volts doesn't seem to be enough to charge the batteries (barely above the 12.61 volt figure) and why do I have only 12.71 volts at the RV batteries when I have 13.78 volts at the the RV supply connection point in the truck bed ?

Thanks for your assistance.

 

[danemayer]

I think there are 2 possibilities. Either the 13.8V from the truck battery is not getting through the umbilical all the way to the trailer batteries, or the ground connection between trailer and truck is partially open.

I'd open the junction box under the trailer pinbox and check voltage there to see if the 13.8V is getting through the umbilical cord. If it's good there, check the thin wires coming back to the mini-circuit breakers near your trailer batteries. One of them is the wire from the truck. It's less likely, but perhaps there's a bad circuit breaker.

Also check continuity of the ground wire in that box under the pin, all the way back to the truck's negative battery terminal.

 

[NWILSON]

Also check continuity of the ground wire in that box under the pin, all the way back to the truck's negative battery terminal.

Wouldn't there be no lights or brakes if there was a problem with the truck to trailer ground?

 

[LBR]

I would start by thoroughly scuffing all 7 connections on both the truck and cord plugs...clean with DeoxIT....check the blades in the cord plug....etc.

Could be a bad connection on the 2 charging connectors, thus the reason your voltage only rose up a tenth of a volt.

 

[danemayer]

Wouldn't there be no lights or brakes if there was a problem with the truck to trailer ground?

Maybe a lousy ground connection would provide enough current flow for the lights, especially if LEDs. As for brakes, they must have a different ground path because they will operate from the breakaway circuit, without a connection to the tow vehicle.

I seem to recall someone who had a problem with the ground wire in the truck harness to the 7 pin connector, and sometimes they'd get a ground through the hitch; other times not.

 

[NWILSON]

Maybe a lousy ground connection would provide enough current flow for the lights, especially if LEDs. As for brakes, they must have a different ground path because they will operate from the breakaway circuit, without a connection to the tow vehicle.

There is no separate ground for the brakes. The breakaway switch takes power from the ship's battery (or it's own battery if the trailer does not have a built in) and routes it to the same wire that comes from the 7 pin plug. There is just 2 wires on the switch (power in and power out). If the trailer's brakes and lights are working, the ground from the truck is good.

 

[dave10a]

There are several possiblities depending on year and manufacturer of the truck. Some trucks have fuses and others have relay and circuit breakers that supply charging power to the trailer. Grounding can be a problem as well an open hot wire connection, fuse, circuit breaker or relay. The newer Ford's for example would provide and error message for some but not all situations. However multimeter tests at several locations is the best method to troubleshoot an electrical problem. That requires testing at the various connection and breakout boxes. BTY if there is a short somewhere the vehicle fuse or circuit breaker will pop instantly. Generally those fuses/circuit breakers at 25amp.

 

[danemayer]

There is no separate ground for the brakes. The breakaway switch takes power from the ship's battery (or it's own battery if the trailer does not have a built in) and routes it to the same wire that comes from the 7 pin plug. There is just 2 wires on the switch (power in and power out). If the trailer's brakes and lights are working, the ground from the truck is good.

No point arguing. Test or don't test.

 

[TomMar]

For my 2cts I would start . at the 7 pin connector and verify what was coming from the truck.

The two batteries in my 2008 Big Horn RV do not appear to be being charged by the truck but are being charged on shore power, here is some data, please advise recommended checks and remedies, thank you.

Truck disconnected from RV, RV connected to AC shore power.
13.2 Volts at both RV batteries

RV not connected to truck or AC shore power.
RV battery on right side 12.62 volts
RV battery in front compartment 12.61 volts

Truck at idle, RV connected to truck not connected to AC shore power.
Left drivers side battery in truck 13.80 volts
Right side truck battery 13.79 volts
Voltage at truck output in bed 13.78 volts
RV battery on right side 12.71 volts
RV battery in front compartment 12.71 volts

I think this is the key point, 12.71 volts doesn't seem to be enough to charge the batteries (barely above the 12.61 volt figure) and why do I have only 12.71 volts at the RV batteries when I have 13.78 volts at the the RV supply connection point in the truck bed ?

Thanks for your assistance.

 

[mrcomer]

On my old 2003 Chevy I had to install the fuse that would let the truck charge the trailer. There was no fuse installed in the truck from the factory, not sure why but that is the way it was.
Good luck,
Mark

 

[wdk450]

My truck has a 25 amp fuse in it's engine bay fusebox for trailer battery charging. I am not sure that the pins in the 7 way connector are up to handling 25 amps.

I have heard of RVers who were concerned with this installing DEDICATED cables in their trucks, using larger gauge wire, going to a separate larger gauge 2 wire umbilical cable to the trailer to bring full current and a good ground directly from the truck engine compartment to the trailer. A voltage indication LED at the truck side of the umbilical connector will let you know if the truck charging fuse has blown.

 

[DickO]

Not sure what brand truck you have. Had same problem with my 2008 Chevrolet. Come to find out there was a connection for the wire to charge the trailer battery under the truck that was never connected at the factory.

 

[DougKirby]

I think there are 2 possibilities. Either the 13.8V from the truck battery is not getting through the umbilical all the way to the trailer batteries, or the ground connection between trailer and truck is partially open.

I'd open the junction box under the trailer pinbox and check voltage there to see if the 13.8V is getting through the umbilical cord. If it's good there, check the thin wires coming back to the mini-circuit breakers near your trailer batteries. One of them is the wire from the truck. It's less likely, but perhaps there's a bad circuit breaker.

Also check continuity of the ground wire in that box under the pin, all the way back to the truck's negative battery terminal.

Hi Dan, you were 100% correct thank you - the issues were a broken earth/ground wire and a faulty connection in the male plug of the umbilical cord. Regards Doug.