Running Hot Wire To 7 Way Trailer Plug?
 

My hot wire (to charge batteries on trailers) does not work. I've tested all the wires with the key on and with the truck running and am not getting any power. The fuse is good. I can't locate the relay for the hot wire. The manual shows it, but it' not there. I'm just going to run a fused hot wire from the battery back to the 7 round. What size fuse should I use? What color wire do I tap into? Is it ok just to run it off the truck battery or will this drain my batteries?

Did it ever work? Reason for asking is that the fuse and relay for the charging circuit wasn't installed with the tow package. You say that you found it in the manual but can't find the fuse and relay locations?

The fuse (30 amp I believe) is located in the power distribution box (PDB) under the hood (driver's side against the firewall). Your manual will tell you which slot. The relay goes in the small black box attached to the side of the PDB (there are two boxes - I think it's the one closest to the firewall).

Hope that helps.

if the relay is not there, then it won't work.. plug in the relay and you'll be done.. same thing happened to me on my 06 F150.. simple change
the relay protects the truck side of the harness in case of dead short..
Sam

I'm not sure if it ever worked. The previous owner had hacked of the trailer plug. There is a 30 AMP fuse in the correct spot in the power distribution box, but there are no relays attached to the PDB. I've got everything working except for the hot lead, so I have turn signals and running lights. I'm going to be buying a car trailer in the spring so I want to make sure everything is working. If I have to run a hot wire, I will.

all of those other circuits run through relays in the same location... so they must be there.

unless someone took it out.. and didn't out it back.. it just plugs in..

3-4 bucks at autozone, walmart, etc.. and you plug the new one in..

or, this vehicle was built without the trailer stuff. (don't know why) but they would have left out the relay without the rear connector

Sam

I'll check again, but I did look for it and know what I'm looking for. It wouldn't be in the fuse box under the dash or anything like that, right?

Here's a pic of what you're looking for. The relay box with the cover removed is the one that will host the charging relay.

https://www.ford-trucks.com/user_gal...id=234011&.jpg

you know. I don't know if 99's had it all wired from the factory..
(I'm having a heck of a time looking at the online manual)

just previous post seems to say yes

Sam

I'm pretty sure the OP's '99 PSD is the same as my brother's '00 PSD and his fuse box and relay boxes were in the same locations as mine.

My 99 had originally 6 prong receptacle with no hot wire. I found empty fuse space for 30 amp fuse and wire with taped end attached to the frame. It all work once connected.
I think it was white or orange, since not too many manufactures observe the black/red code. Look for #10 wire attached to the frame along the wire harness.

I'll give this all a check, but it's raining like cats and dogs out now, so it'll have to wait!