12 volt from truck

[Garypowell]

I have known for a few weeks that the 12 volt back to the trailer wire connector on my truck was never connected by the factory. So I searched it out and connected it. Checked it out and I now have power back to the connector on my bumper.

I thought this "power" would somehow charge my battery while towing. My simple test was to leave the lights on in the unit while towing in hopes of seeing a full battery 3 hours later. I did not.

So next pull once I arrived before I hooked up shore power I left trailer hooked to the truck and turned the battery disconnect switch off to remove the battery from the circuit. The whole 12 volt system went dead.

What am I missing here?

1 does the 12 volt that is at the bumper plug really not connect into the trailer 12 volt system like I thought it would?

2. Or is something not hooked up right in the RV?

thanks

 

[danemayer]

Re: 12volt from truck

Gary,

I guess "12 volt system went dead" means interior 12V lights went out when you turned the battery disconnect.

There is a circuit breaker in between the battery and the power converter/wiring to the fuse box. If that breaker has tripped, you might be getting power to the buss bar, but not to the fuse box. If you have a meter, you could probably check for voltage at the buss bar with the battery cut off and shore power unplugged.

Here's a link to our 12V troubleshooting guide which may be helpful.

 

[Bob&Patty]

Re: 12volt from truck

Gary, #1 it may take awhile to charge the battery when towing. This is depending on its state of charge and internal condition.

#2. when you disconnected the battery, you shut off the 12V to the coach. The coach battery supplies all the 12V for the coach. Not the truck....the truck provides the 12V to charge the battery and run all the marker,stop/brake lites and the brakes.

 

[Garypowell]

Re: 12volt from truck

Maybe I am not making myself clear. By having full time 12volt supplied now to the plug at the back of the truck and the RV cable plugged in would this 12 volt would supply the 12 volt system in the inside of the RV? So if I removed the RV battery everything would continue to work.....frig on gas, lights, furnace, etc. thinking this would be an emergency supply if something happened to my battery in the RV. Again this theoretical discussion assumes no shore power.

i understand that prior to hooking up the dedicated 12 volt line to my plug on the truck that 12 volts still ran down this cable to run my breaks, outside marker lights, etc. but I thought once I connected the dedicated 12 volts it would/could power the inside stuff too.

i have looked at the schematics but it does not show where the truck 12 volt comes into the RV distribution system. Dan spoke of a "breaker" but again there is no place that points out where the truck 12 volts comes into the "inside" 12 volt system. The diagram only shows the RV battery not the truck battery.

Gary

 

[brianharrison]

Re: 12volt from truck

Check out this diagram. The 12V from truck comes in "upstream" of the battery disconnect. Switching this to off isolates the 12V system from battery and charge from truck. The diagram comes from here. Brian

 

[Garypowell]

Re: 12volt from truck

Brian,

that's what I needed....thanks!

I thought I had looked at all of the diagrams but had not. At least I now know it is supposed to work the way I envisioned. But I defeated my purpose the way I conducted the test.

My RV is still up in Williston (FL chapter rally) and won't see it for another 2 weeks but now I know I can simply unhook the battery to see if all is well with the truck 12 volt getting used. And if it is not then I can figure it out from there.

Thanks to all for your input!

 

[wdk450]

Re: 12volt from truck

Gary:
If you have a DC voltmeter you can take 2 battery readings to see if your truck charging wiring is working. Take 1 reading trailer unplugged from truck (and not connected to shore power). Take a 2nd reading with the trailer cable connected to the truck with the truck engine running. The 2nd reading should be higher.

You can make a resistance check from pin #4 on the trailer connector to the positive terminal of the battery to check if the +12 volts trailer wiring is connected. I assume your lights and brakes work O.K. so we can assume the trailer cable ground wiring is O.K.

The amount of amps of charge the truck can supply to the trailer battery is limited by a fuse in the truck, and the wire size of the associated wiring in the truck and trailer. The charging voltage is on pin 4, on right the top of the truck connector to ground (pin 1 on the left bottom of the connector). Google an image of an "RV 7 pin connector". I tried to attach that to a reply I composed last night and the forum locked up.

You might want to check out your batteries, too.

 

[Bob&Patty]

Re: 12volt from truck

Gary, I just thought of this. If the wires where not connected in the UBC under the hood....then maybe the fuse is not installed either. Look at the diagram on the UBC lid. It will show you where the fuse goes and you can see if the fuse is in place. They will be the square fuses that are colored. I think it is a 50 amp fuse. Normally when you get the truck new....the fuse should have been in the glove box with the 7-4 plug.

 

[Garypowell]

Re: 12volt from truck

Thanks again all. The truck has a 30 amp fuse and there was power there to the correct pin at last checking. Just could not figure out why I could not see any results in the RV.

I don't know about you guys but sometimes my 2 + 2 does not add up to four. So I wanted to be sure it should work before I tore things apart.

Of course now I know it should work and was just using a wrong method to check. Two weeks from today we start our next six week sales trip and will take this good help with me to make sure all is ok and working as it should.

Thaks again,