hey guys, have an 04 fx4 with factory tow package. brought home my travel trailer last night from storage and battery was really weak in tt. upon playing with the wires (little loose), and cleaning ended up using mobile charging unit for the battery on the tt. my question is: doesn't the trucks alternator also charge the tt battery when towing? is 10 miles not enough? i tried using a multimeter on the connector on the truck (7 pin), but couldn't figure out which pins to see if it was putting out a charge. help electrical guru's! LOL
thanks

 

I'm no expert, but I don't think 10 miles is nearly enough.

If you are checking with a mm, you probably need the key in the on position. The batt charge circuit on my '99 is on a relay and is active only with key on. This prevents the tow vehicle's battery from being drained by the camper when stopped; if your fridge is on battery power for example. Folks with a direct tow vehicle battery-to-trailer connection usually need to disconnect.

 

When you bought your truck did you find an accessory relay that you were supposed to plug in that allows power to pass to your trailer power jack? Mine was in the glove box with directions to activate this option. Maybe some dealers did this for you OR maybe you did not get one? The relay provides power only when your ignition is turned on. So you would not see any voltage at your trailer jack with the ignition off. You also should have a pin out diagram for trailer jack too.

I do agree with FrankLee that 10 miles is just not enough to bring a discharged battery up to snuff.

 

If you bought the truck new, in the glove box should of been a package with a wiring harness and a relay in it. The relay is a "Trailer Tow Battery Charge Full ISO Relay", which needs to be plugged in the fuse block so the truck will charge the battery. The fuse block is located under the passenger side kick panel in the footwell. If you can't find the relay, check the fuse panel to see if it has already been installed.

 

now that you mention it, i do have that wire in the glove box....never knew what it was for. thought it was for the brake controller. (have a prodigy and wiring kit.) it has alot of wires and a small box of some kind. do you have specifics on the install? i have an 04 ford with the 5.4.....on a side note, the wiring must be ok, when plugging into the house i get 13.9 at the battery! thanks for the tips so far.

 

Thank you. I have been wondering what that wire and relay were used for. They have been in my glove box for 15 months and I never knew what they were for. You guys are awesome!

 

Mine was in a sealed plastic bag with an instruction sheet included. I guess some dealers are short on support or just not aware of their product.

 

I always thought it would take about 25 mls. too charge a battery up while driving

 

The wiring harness is for a brake contoller when you have a large trailer with electronic brakes. There should also be the relay in the bag. It looks like a small cube with metal prongs sticking out of it. That is the charging relay. You need to plug that in so your seven pin plug for your trailer lights will also have a hot lead to charge your battery on your camper

 

thanks guys! i was under the impression that as a factory tow package everything was already taken care of. i looked in my little plastic bag and did indeed find the relay! plugged it in this morning at work and just checked it tonight with the meter in the 7pt plug. reads 0 with key off, 12.9 or so with key on, and 13.9 when truck is running.....these boards can be a life saver.....thanks again....getting ready to tow our tt up to the catskills with the bike in the back! wanted everything to be correct! see ya...

 

Why does this relay not come installed from the factory? Can one install it and run it all the time, or should it only be installed and used when needed?

 

LOL, same thing here. Now I know what it is for.

 

don't know why they just don't install them at the factory. As far as I know, it can stay in. My realy has been istalled for a few months without a problem, and in my lst truck I had it in for a year, no problem.

 

I would think if this was installed and you launched a boat and the trailer harness were to go under water it could pose a problem.

Maybe thats why you have to install it..

Dunno.