I dont have a tow package, but I noticed the 5amp fuse for the relay is in the fuse block. I haven't looked to see if the relay is actually there yet.
What guage, color and where would the wire be located for the trailer battery charge relay?

'03 E350

 

I have an E150. My relay came with the cable to connect the full 7pin trailer plug. I ordered it from Ford. The relay went in under the hood in the fusebox. The cable connected in near the rear spare tire on the drivers side. it replaced the 4pin towing plug cable as well as had a second plug (for the BAT, TRAILER BRAKE, and backup light)

Cannot tell you what the charge relay wire is, but hope the helps! If you find the charge relay wire let me know.. been looking for it myself.

 

I think you'll find that the BAT lead is what charges the trailer battery. You would have to make sure that it can supply adequate current for your needs (I think they're fused at 30 amps), and, if you don't have an isolator, that you don't discharge your starting battery.

 

If you use the trailer battery charge relay, then you don't need an isolator.

 

The charging to the Aux battery would be switched special so it isn't on all the time.
Only when the relay cuts in.

 

So, without an isolator and using the trailer battery charge relay only, the auxilary battery can be over charged?
What would the voltage and the current be to the auxilary battery be? assuming the starting and the aux. battery are fully charged.
I plan on using a 75 ah gell battery or I can use sealed lead acid.

 

You can consider all the batteries being connected as one when they are charging. With an isolater, it will let the aux battery(s) be freely charged that are hooked to it, but won't let them be discharged backwards through the isolater. So the only way the aux battery can be discharged is by a load connected directly to the aux battery.

You can consider the batteries like water tanks. And the lower the water level (charge) of the tank(battery), the more water flow (current) you will have to that tank(battery). The water tanks(batteries) that are full (charged) will draw no water(current).

 

Here is another thing people don't understand.

The aux battery should have Some Drain on it,because if all that happens to the battery is Charging it, it will end up sulfating from over-charging and lack of discharge.

I run the stereo to the truck & under the topper off my Aux Battery just for a small drain.

 

I still can't find the wire. Did the harness you get plug in at the frame rail by the spare tire?

 

cocot-
the second plug was part of the van harness running along the drivers rail. as I remember it, it was near the spare alittle toward the front of the vehicle. if you have the 4 pin trailer plug, trace it from the rear of the vehicle, the second plug was very close to where the 4pin line plugged into the harness. it was 3-4feet from the end of the 4pin wire. hope that helps! let me know if you still do not find it and I will go out and crawl under to find mine again. Gotta go preach this morn.... happy Easter!

 

Good Sun Morning... now back to the details.

the plug is immediately behind the axel in the rail on the drivers side. it has a white wire comming out of it going directly to frame ground about 8 inches away.

One plug:

Orange - Battery feed
Black w/green stripe - trailer backup lights
White - ground
dark blue - trailer electric brake

the other plug (this should have the 4wire trailer plug cable to it)

Yellow - Trailer LH turn & brake
Dark Green - Trailer RH turn & brake
Brown-White - trailer run lamps

the wiring diagram shows the Bat feed (orange) to be that color all the way back to the relay under the hood

since I cannot post attachments (at least I have not figured out how) to find the trailer bat feed relay look at the relay fuseblock on the drivers side under the hood

as you stand on the drivers side and face the relay it will look like this


F F F F F F
R f f f f f f f <- larger fuses
O xx xx z z <- small relays diode little fuses
N XX XX XX <- the right relay is the trailer bat feed relay
T XX XX XX <- these are the large relays

Drivers side



if the relay is not there you will need the relay "F0AB-14B192-A"

that help any?

 

I stuck my nose under there and I see that the flat 4 pin connector plugs into a round connector on the frame where you are talking about. The other plug is not there. There is a plug on the drivers side by the axel that has a red and a br/g wires. I tested for 12 volts which is present, but when I pull the relay the voltage is still there, so that ain't the one. Maybe it's different for 2003?
I do thank you for all your help!

 

gonna figure this out yet!

on my vehicle, there is 1 wire bundle comming back from the front of the vehicle.

in front of the axel two wires peal off to go to the differential housing (the speed sensor)

then ~6inches later three wire bundles peal off.

two are the trailer plugs as described above.

the last is a two wire (red and purplew/ white stripe) going to a round cylinder mounted on the frame rail next to the spare. it appears to go to a sensor for a air (vacume?) storage tank.

the best clue is the white wire going to the channel frame ground from the plug with the Bat feed if you have it.

if you have the relay under the hood (mine came with the trailer wire extension bundle I purchased to go from the axel to the rear bumper) a thought is to peek into the wire bundle in front of the gas tank to see if the orange wire is there, or even harder peek into the wire bundle next to the underhood fuse box. my diagram says it should be there.

but of course they could have changed the wire colors just to mess with us!

I would think if you have the relay you should have the plug back there, hopefully it is just not hiding well!

happy hunting!

 

I didn't have the relay from the factory. I bought it from Ford.
Armed with the info that you have supplied, I will look under there again and let you know what I find.
Thanks

 

Thanks somebody for pointing me to this thread. Regarding the drain on the RV battery: I don't have one. We don't use the camper enough to keep one on it (a pity, I know!) so we use the constant hot to power the refrig and stuff while we're towing. This relay will continue to give me constant power, even if there's no battery attached, won't it?

Thanks!

Hal