Truck to 5er DC

[friz]

Plug connecting the truck to the 5th wheel doesn't have 12 vdc (truck side) I think it was pin 7 but I would have to check the diagram to be sure. All other pins have the needed voltage and the brakes, tail lights and running lights are all working when connected. I made the assumption that the 12 vdc pin was supplying voltage to the 5th wheel battery to charge it.
So, what would a 12vdc hot pin actually be used for in the 5th wheel? Is it actually needed?
If I need to put power to it what would be a good source on the truck? There is plenty of 12 vdc around the tail gate/bumper area. It would be a long run to the cab fuses or engine batteries. A little work but buy all means "doable"
For the record we took a 2 month trip last year with this condition. We never "boondocked" long enough to drain the battery. If we had, I assumed the 12 vdc from the truck would have recharged the house battery as we drove if it was hot?
Thanks, Friz

[Notanlines]

Friz, if you are driving a GM product, it is quite likely that you will have to hook up that wire yourself. On older models is was a red wire (loose) hiding under the brake master cylinder. If you Google this problem they will show you which spot (empty and no fuse either) in your under the hood fuse box it goes.
Go here: https://www.youtube.com/watch?v=IPk6DITVvh8

[Begger]

On some models, the truck key has to be in at least the accessory position, if not running. Or, the start button has to be in the accessory position.

Just a thought...

[wingnut60]

Ok, you have a Ford? Have the owner manual with the fuse layout? There are 2 of them--one behind the passenger kickpanel front seat, and one in the engine compartment on driver side near firewall. This one in the engine compartment contains the fuses for the trailer components--look there for a fuse via the owner manual that controls the 12 volt power to trailer.
You will never do any better than keeping up a well-charged battery with the alternator--too long a wire run, too small a gauge wire, almost no amps left for the trailer.

[friz]

The truck is a 2004 Ford F-250 diesel. I will have a look under the hood for the fuse box. Thanks, guys, getting closer!
Okay, looked at the Owner's Guide for my truck. Fuse/Relay position 115 (if there), 20 amp fuse for "Trailer Tow Battery Charge". Only fuse panel/box mentioned is in the cab.
If it is hot when the ignition key is on or engine running, I suspect (hope) there is a terminated wire in the bumper area not connected.

[Photomonjax]

I had this problem on a 2009 chevy 2500. Never hook up at the factory but the dealer hooked it up after a few dead batteries.

[MTK46]

If the fuse is there the wire should be connected at your trailer plug.
I had a 03 & 05 Ford F-350 in the past & they all had the 12v power wire at the trailer plug. My son has a 03 F-250 and his also is wired

[Edd505]

Lots of bad info, your 3/4 ton will be exactly like this, give it a try:

your 2004 Ford F-350 and was able to find that the trailer tow battery charge/12V power circuit fuse is located in the number 115 position and is a 20 amp fuse. There is also a trailer battery charge relay located in the number 305 position. The fuse/power distribution box is below and to the left of the steering wheel, by the brake pedal. In order to access the fuse box, you will need to remove the panel cover.

Additional fuse and relay locations related to trailer towing on your truck are as follows:

Number 6 position - 20 amp - Trailer Tow Turn/Stop Relay
Number 38 position - 20 amp - Trailer Tow Parking Lamps
Number 39 position - 15 amp - Trailer Tow Backup Lamps
Number 101 position - 30 amp - Trailer Tow Electric Brake

[friz]

Lots of bad info, your 3/4 ton will be exactly like this, give it a try:

your 2004 Ford F-350 and was able to find that the trailer tow battery charge/12V power circuit fuse is located in the number 115 position and is a 20 amp fuse. There is also a trailer battery charge relay located in the number 305 position. The fuse/power distribution box is below and to the left of the steering wheel, by the brake pedal. In order to access the fuse box, you will need to remove the panel cover.

Additional fuse and relay locations related to trailer towing on your truck are as follows:

Number 6 position - 20 amp - Trailer Tow Turn/Stop Relay
Number 38 position - 20 amp - Trailer Tow Parking Lamps
Number 39 position - 15 amp - Trailer Tow Backup Lamps
Number 101 position - 30 amp - Trailer Tow Electric Brake

Thanks Edd505 et al, you guys were a great help in fixing this. It turned out to be the 20 amp fuse. Put a new one in and 12vdc appeared on the bumper plug pin when key is in the "Run" position. My stating there was not a wire on the Trailer 12vdc pin was a mistake. Anyhow next step is to plug the 5er into the truck and see if the fuse blows. I suspect it was blown when I bought the truck years ago. At least I hope it was. Once again, thanks for the assist