2005 expedition 7pin harness installation

[brodi3man]

My 05 expedition came factory with the 4pin trailer harness.  I purchased this http://www.etrailer.com/Wiring/Hopkins/37185.html to upgrade to the 7 pin.  i have the ground, brake, and aux(reverse lights) wires installed but am stuck on the 12v power lead.  I could run a new wire from batter to hitch with a fused connection.  I'm hoping the 12v lead wire is back there just hiding somewhere.  All the other wires were already back there just waiting to be found.  You all rock!  thanks for the help in advance. 

Brodie

 

[brodi3man]

Found this statement on a ford truck forum and was wondering what your opinions are.  The more i research the more im thinking i dont need that 12v lead as much as i thought. 
Do you all charge the camper battery another way then?

//post from ford forum//
Trailer battery charge is next to useless because the charge rate drops to less than an amp after a few minutes. The voltage regulator in the truck only lets the voltage get high enough to charge the truck battery and the voltage drop thru the wiring to the trailer drops it even further. I've measured this charge at the the trailer battery and no effective charging is occurring, just battery maintenance. The little Group 24 battery on most camper tongues only has about 55 useful amp hours (the 80 amp hour label includes volts below 11) and at under an amp would take 100 hours to fully charge as the charge rate gets even lower than an amp as the battery approaches full charge
//end post from ford forum//

 

[rbell]

The camper battery will charge from the built in charger. But your Expedition can also charge it. As for that statement they made 11vdc is way beyond dead. A dead (fully discharged) 12 volt battery will still measure between 11.6 & 11.8 vdc. fully charged they measure 12.6-12.7. So when your TV battery gets fully charged it'll drop back to a maintainence level probably about 13.1 or 13.2. Most will charge up to about 14.5 when needed.
An Expedition needs to have a fuse and a relay installed to get 12v at the rear. The relay opens when the ignition switch is off so the trailer doesn't draw on the TV at night and run the battery down. The fuse protects that circuit. If you look at the cover of the box you may be able to figure out which spot they go in. I don't remember. Both my Expedition had towing packages and the stuff was in a plastic bag packed with the jack in the back. The F-150 I have now had it in the rear door compartment. The owners manual has a chart with some of that info also, but it's a bit hard to interpret.

 

[Gary RV_Wizard]

The point about 11v is that the 20 hour rate procedure used to come up with the battery amp hour rating includes discharge all the way to 10.5v. Amp hours at voltages under about 11.5 aren't really useful inmost cases because the voltage is too low to do much other than put a dim glow on a light bulb.

I would expect the 12v line on the connector to produce about 13.0-13.4v with the alternator running (typically 14.4v output). If it didn't, I'd be looking for a bad connection or under-sized wiring.